There is a thorough post I saw earlier this year that covers the Vanguard program and has links to posts discussing the similar programs at Fidelity and Schwab. Search “WCI Vanguard Fully Paid Lending Program”.
I researched the Schwab program and it’s not as good as it sounds. You basically split the 10% interest rate with Schwab. No way would I go 50/50 on a partnership if I am putting up all the $ and taking all the risk.
Same not worth the risk, though I don’t understand margin investing especially since I can pay a lower interest rate with stock options and have less risk