How to invest 500k ? Real estate multi family or other

Hey Everyone ! Just want others opinion on this

If you have 500k , what would you invest in to generate good cash flow ? Stocks , multi family , other creative investments ? Preferably 10-20% return

A quick summary of me , self employed with stable income , I have 35 units already of multi family that generate decent cash flow but can’t seem to find any new decent deals in this market for 2021 . Currently owe roughly 2.5 mill on mortgages and primary home , if paid off , that can add another 22k in cash flow if all mortgages paid off . What would you do ? I’m Fairly young as well . I have no stocks or 401k or retirement savings .