[alteria]

Excellent explainer that's worth a read [1] and it's HN thread [2]

tl;dr: Interest, payment for order flow, and securities lending (but mostly interest)

[1] https://www.kalzumeus.com/2019/6/26/how-brokerages-make-mone...

[2] https://news.ycombinator.com/item?id=20276551