As someone in the financial industry, I can throw out a few suggestions. These vary substantially depending on your level of interest, time, and risk-tolerance. I am not a financial advisor, nor should you consider any of this professional investment advice. I know your question is geared toward resource and learning. I will address that, but I'll also include the easier options if you decide to just say screw it and go the simple route. That being said...

You could go the low risk, low-cost, near-zero time method of using index funds. For full disclosure, this is the area of the industry I am involved with. You can either choose the funds yourself or you can get someone to provide you some suggestions. There are advisors out there who specialize in tactical weighting of a defined set of index funds (i.e. the funds you have available in your 401k for example). They vary the weights usually on a quarterly basis on a set of criteria that is proprietary to them. This tactical weighting can outperform the market if they know what they are doing. They will, however, charge the standard advisory fee for this.

You could just hand over the reigns to an advisor after speaking to one your are comfortable with. they'll charge their standard rate and if they are halfway decent they will match your investments to your risk profile/tolerance. Be wary, though, as many may just shovel you into a default set of index funds. If you pay an advisor you need to be sure they actually add some sort of value and that they adhere to fiduciary standards (not "suitability" standards)

if you actually want to focus on individual stocks, please please please at least learn the absolute basics about fundamental ratios and how to look at a balance sheet or cash flow statement. Or actually know the company you are investing in. There are many books out there. The gold standard about value investing is Ben Graham's famous Intelligent Investor.

real estate is a fairly tried and true method. investment properties produce reliable cash flow. there are property management companies out there that will charge usually around 10% of the rent to keep your place rented and handle the landlord duties.

you could also focus on a stock market strategy geared toward passive income. something like a covered call strategy. that is a strategy commonly used in a sideways market or a market not strongly trending in either direction to produce cash flow by owning the stock and issuing/writing a call against it where you collect the premium. A few books I have read that offer some good intro to the basics of options strategies (and a few slightly more advanced methods) are the followings ASINs on Amazon - B014C59R9S, B01EPJC2T8, B0165YDUSS, and B00YBIK9P8. They're short and very straightforward to help understand the basics and also generate some ideas for yourself. They're only like $3 a piece, too.

moving up the ladder of education and effort - you could pay for training courses for a site like WallStreet Mojo. I happen to have purchased all their stuff in a recent sale they had (like 85%+ off), which they have from time to time. They also have some free stuff for you to check out. It looks like they are running a special right now on the premium courses. Not sure how long that is in force. https://www.wallstreetmojo.com/courses/ They have courses targeted for investment banking, CFA, financial modeling, etc. Their courses include videos and downloadable Excel templates/examples to learn with. It's time consuming, but if you are actually interested in how the financial analysts and investment bankers perform valuations then it's a pretty solid tool/resource. Their CFA courses are obviously geared toward the CFA exam, but the knowledge is the same and can be applied in any way you choose. You would be able to skip the compliance and ethics portions and just focus on the rest. this information combines to form a much more in depth valuation toolbox and you could theoretically choose stocks with success using careful analysis, or perhaps create fund-style strategy to spread out the risk of your personal portfolio.

you could also purchase an existing business that is for sale. they are plenty of sites dedicated to these sales. if you find something you like, get an attorney who knows about these transactions. this basically is a sort of turn-key solution that provides relatively predictable cash flow. but it's not quite turn-key as businesses require work and you already own/run one. if you decide to go this route, i would suggest making sure the cash flow has enough wiggle room to hire someone to replace your own involvement, as you likely won't have the time to run it yourself.