What are your thoughts on an Immediate Annuity as a passive income vehicle? I suppose it’s not a great investment since you never get your principal back, but the risk is zero and the cash flow is fairly good, approaching 6% currently. And, since you are guaranteed payments for life, you may not care that you never see your principal again anyway since you’ll be dead!

The appeal of these passive income sources is that you can diversify across many small investments, rather than in a handful of large ones. When you invest directly in real estate, you have to commit a lot of capital to individual projects. When you invest in these crowdfunded investments, you can spread your money across many uncorrelated real estate ventures so individual investments don't cause significant issues.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.