Inclusion Criteria:  Life expectancy of >= 12 weeks. Histologically confirmed diagnosis of locally advanced and/or metastatic solid tumors that are not amenable to standard therapy. Radiologically measurable disease as defined by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Agreement to provide protocol-specific biopsy material. Adverse Events (AEs) from prior anti-cancer therapy resolved to Grade =<1. Adequate performance status and cardiovascular, hematological, liver, renal and coagulation function. For female participants of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse), use contraceptive measures and refrain from donating eggs. For male participants: agreement to remain abstinent (refrain from heterosexual intercourse), use contraceptive measures and refrain from donating sperm.  Exclusion Criteria:  Known central nervous system (CNS) primary tumors or metastases, including leptomeningeal metastases. Active second malignancy requiring anticancer treatment and/or palliative supportive care. Significant cardiovascular/cerebrovascular disease within 6 months prior to study treatment start. Any other diseases, metabolic dysfunction, physical examination finding or clinical laboratory finding that gives reasonable suspicion of a disease or condition that would contraindicate the use of an investigational drug. Prior allogeneic bone marrow transplantation or prior solid organ transplantation. Active or history of autoimmune disease. Known hypersensitivity to any of the components of RO7300490 formulation or to components of atezolizumab formulation. Pregnancy, lactation or breastfeeding. Dementia or altered mental status that would prohibit informed consent. Major surgery or significant traumatic injury within 28 days prior to the first study drug administration (excluding biopsies) or anticipation of the need for major surgery during study treatment. Treatment with radiotherapy, chemotherapy, hormonal therapy, targeted therapy, immunotherapy or investigational drug concurrent or within 28 days or 5 half-lives of the drug (whichever is shorter) before the first study drug administration.