Inclusion Criteria:  Subject has PsA on the basis of the Classification Criteria for Psoriatic Arthritis with peripheral symptoms at the screening visit. Subject has a history of PsA symptoms for ≥ 6 months prior to the screening visit. Subject has ≥ 3 tender joints and ≥ 3 swollen joints at screening and Day 1 visits. Subject has at least one lesion of plaque psoriasis ≥ 2 cm in diameter, nail changes characteristic of psoriasis, or a documented history of plaque psoriasis. Subject has active PsA despite previous standard doses of non-steroidal anti-inflammatory drug (NSAIDs) administered for ≥ 4 weeks, or traditional disease-modifying anti-rheumatic drug (DMARDs) (including methotrexate and sulfasalazine) administered for ≥ 3 months, or tumor necrosis factor inhibitor (TNFi) agents administered for ≥ 3 months, or subjects are intolerant to NSAIDs or DMARDs or TNFi agents. If subject is on concurrent PsA treatments, they must be on stable doses. For female subjects of childbearing potential involved in any sexual intercourse that could lead to pregnancy: the subject must agree to use a highly effective contraceptive method from screening until at least 4 weeks after the last study drug administration. Highly effective contraceptive methods include hormonal contraceptives (eg, combined oral contraceptive, patch, vaginal ring, injectable, or implant), intrauterine devices or intrauterine systems, vasectomized partner(s) (provided vasectomy was performed ≥ 4 months prior to screening), tubal ligation, or double barrier methods of contraception (eg, male condom with cervical cap, male condom with diaphragm, and male condom with contraceptive sponge) in conjunction with spermicide.  Exclusion Criteria:  Subject has other disease(s) that might confound the evaluations of benefit of NDI-034858 therapy, including but not limited to rheumatoid arthritis (RA), axial spondyloarthritis (this does not include a primary diagnosis of PsA with spondylitis), systemic lupus erythematosus, Lyme disease, or fibromyalgia. Subject has a history of lack of response to any therapeutic agent targeting IL-12, IL17, and/or IL23 at approved doses after at least 12 weeks of therapy, and/or received one of these therapies within 6 months prior to baseline (Day 1). Subject has a history of lack of response to > 1 therapeutic agent targeting tumor necrosis factor. Subject has received infliximab, golimumab, adalimumab, or certolizumab pegol, or any biosimilar of these agents, within 8 weeks prior to baseline (Day 1). Subject has received etanercept, or any biosimilar of etanercept, within 4 weeks prior to baseline (Day 1). Subject has received rituximab or any immune-cell-depleting therapy within 6 months prior to baseline (Day 1). Subject has received any marketed or investigational biological agent, other than those specified in other inclusion/exclusion criteria, within 12 weeks or 5 half-lives prior to baseline (Day 1). Subject is currently receiving a non-biological investigational product or device or has received one within 4 weeks prior to baseline (Day 1). Subject has received apremilast or other non-biologic systemic treatment for PsA within 4 weeks prior to baseline (Day 1), other than methotrexate (MTX), sulfasalazine, corticosteroids, NSAIDs, or paracetamol/acetaminophen, which are allowed at stable doses as described in Inclusion Criterion 7. For subjects not receiving MTX and sulfasalazine at screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1). Subject has received leflunomide within 8 weeks of baseline (Day 1) if no elimination procedure was followed or adhere to an elimination procedure. For subjects not receiving MTX and sulfasalazine at Screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1). Subject has received intraarticular injection (including corticosteroids), intramuscular steroids, intralesional steroids, or intravenous steroids within 4 weeks prior to baseline (Day 1). For subjects not receiving MTX and sulfasalazine at screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1). For subjects not receiving MTX and sulfasalazine at screening, MTX and sulfasalazine are excluded within 4 weeks prior to baseline (Day 1). Subject has received high potency opioid analgesics (eg, methadone, hydromorphone, or morphine) within 2 weeks prior to baseline (Day 1). Subject has used any topical medication that could affect PsA or psoriasis (including corticosteroids, retinoids, vitamin D analogues (such as calcipotriol), JAK inhibitors, or tar) within 2 weeks prior to baseline (Day 1). Subject has used any systemic treatment that could affect PsA or psoriasis (including oral retinoids, immunosuppressive/immunomodulating medication, cyclosporine, oral JAK inhibitors, or apremilast) within 4 weeks prior to baseline (Day 1). Subject has received any ultraviolet (UV)-B phototherapy (including tanning beds) or excimer laser within 4 weeks prior to baseline (Day 1). Subject has had psoralen and UV A (PUVA) treatment within 4 weeks prior to baseline (Day 1). Subject has received Chinese traditional medicine within 4 weeks prior to baseline (Day 1) Subject has received any live-attenuated vaccine, including for COVID-19, within 4 weeks prior to baseline (Day 1) or plans to receive a live-attenuated vaccine during the study and up to 4 weeks or 5 half-lives of the study drug, whichever is longer, after the last study drug administration. Subject is currently being treated with strong or moderate cytochrome P450 3A (CYP3A4) inhibitors, such as itraconazole or has received moderate or strong CYP3A4 inhibitors within 4 weeks prior to baseline (Day 1). Subject has consumed grapefruit or grapefruit juice within 1 week prior to baseline (Day 1). Subject has used tanning booths within 4 weeks prior to baseline (Day 1), has had excessive sun exposure, or is not willing to minimize natural and artificial sunlight exposure during the study. Subject is a female who is breastfeeding, pregnant, or who is planning to become pregnant during the study. Subject has evidence of erythrodermic, pustular, predominantly guttate psoriasis, or drug-induced psoriasis. Subject has a history of skin disease or presence of skin condition that, in the opinion of the investigator, would interfere with the study assessments. Subject has any clinically significant medical condition, evidence of an unstable clinical condition, psychiatric condition, or vital signs/physical/laboratory/ECG abnormality that would, in the opinion of the investigator, put the subject at undue risk or interfere with interpretation of study results. Subject had a major surgery within 8 weeks prior to baseline (Day 1 or has a major surgery planned during the study. Subject has a history of Class III or IV congestive heart failure as defined by New York Heart Association Criteria. Subject has an estimated creatinine clearance of < 40 mL/min based on the Cockcroft-Gault equation or a history of renal failure. Subject was hospitalized in the 3 months prior to screening for asthma, has ever required intubation for treatment of asthma, currently require oral corticosteroids for the treatment of asthma, or has required more than one short-term (≤ 2 weeks) course of oral corticosteroids for asthma within 6 months prior to baseline (Day 1). Subject has a history of cancer or lymphoproliferative disease within 5 years prior to baseline (Day 1). Subjects with successfully treated nonmetastatic cutaneous squamous cell or basal cell carcinoma and/or localized carcinoma in situ of the cervix are not to be excluded. Subject has a history of fever, inflammation, or systemic signs of illness suggestive of systemic or invasive infection within 4 weeks prior to baseline (Day 1). Subject has an active bacterial, viral, fungal, mycobacterial infection, or other infection (including TB or atypical mycobacterial disease), or any major episode of infection that required hospitalization or treatment with intravenous antibiotics within 12 weeks prior to baseline (Day 1), or oral antibiotics within 4 weeks prior to baseline (Day 1). Subject has a history of chronic or recurrent infectious disease, including but not limited to chronic renal infection, chronic chest infection, recurrent urinary tract infection, fungal infection (with the exception of superficial fungal infection of the nailbed), or infected skin wounds or ulcers. Subject has a history of an infected joint prosthesis or has received antibiotics for a suspected infection of a joint prosthesis, if that prosthesis has not been removed or replaced. Subject has active herpes infection, including herpes simplex 1 and 2 and herpes zoster within 8 weeks prior to Day 1. Subject has a history of known or suspected congenital or acquired immunodeficiency state or condition that would compromise the subject's immune status (eg, history of splenectomy, primary immunodeficiency). Subject has positive results for hepatitis B surface antigens (HBsAg), antibodies to hepatitis B core antigens (anti-HBc), hepatitis C virus (HCV), or human immunodeficiency virus (HIV). Samples testing positive for HCV antibodies will require polymerase chain reaction (PCR) qualitative testing for HCV RNA. Subject has clinical or laboratory evidence of active or latent TB infection at screening as assessed by QuantiFERON-TB Gold (or a purified protein derivative [PPD] skin test or equivalent, or both if required per local guidelines) and chest X-ray. The PPD skin test should be utilized only when a QuantiFERON-TB Gold Test is not possible for any reason (unless local guidelines require both tests). Chest X-ray may be taken at screening or completed within 3 months prior to the screening visit, with documentation showing no evidence of infection or malignancy as read by a qualified physician. Subject has a known or suspected allergy to NDI-034858 or any component of the investigational product, or any other significant drug allergy (such as anaphylaxis or hepatotoxicity). Subject has a known history of clinically significant drug or alcohol abuse in the last year prior to baseline (Day 1).