> Is Coinbase "loaning" out the Bitcoin users have deposited in it?

Maybe not Bitcoin, because I don't know if Bitcoin has any staking protocols in it.

But things like Anchor / UST / Luna participated in a staking scheme, where if you promised not to sell UST, you'd get 20% APY gains (measured in UST of course, not US-dollars).

Coinbase could be participating in those schemes in a group wallet-setting. Ex: UST holdings at Coinbase would be staked, so that Coinbase would get those gains. Or with other coins with such benefits??

I'm mostly pulling this out of my ass btw. I don't know the structure of Coinbase. But I can see the "incentivizing" from the various cryptocoins on the market or the various "protocols" that allow for exponential growth (as long as you "lend" or "stake" your coins somewhere else).