Okay.. So many different opinions and advice. (Most of which seems self serving)
Here is mine- First off I don't get mortgages either. I own 25 properties and none have loans.
My properties are either high cap rates in C or D areas that return 10-20% cash on cash or in nicer B grade areas that are steady good tenants that return 7-9% and appreciate more in Value than the cash flowing c/d area rentals.
It really boils down to how involved you want to be in the rental / investment process.. Based on the fact that you are in your 20s live in Silicon Valley and have $500k I'd say you are probably busy with your day job and don't really want to be involved with flipping and STRs that take a lot of oversight.
I would NOT buy in California.
I would personally not invest in syndications. (If you are considering this ask if they leverage their properties with your investment.. Investing in this may also violate Sharia law )
I would either buy out state in a lower income area if you can find someone you trust to sell you the properties and manage them for you. OH, MI, PA, IN, NC or any other lower priced state.
Or if you want more risk and more reward find a flipper that needs an investment partner. I was flipping in the Miami Market and the competition was insane and I could not find anything that made sense to buy so I partnered with a flipper from another area and funded all the flips. Instead of making my normal 20% profit per flip I made 10% after splitting with him but he did all the work on the renovations. It worked out well until his market also became too competitive.