I don't get what the OP means . The name stable coin says that they are stable with some form of Fiat mostly USD . So you are not getting anything by investing in stable coins.
Yes thats right. Maybe what he meant actually is cryptocurrency. Stablecoin in my opinion cant be considered as investment if you wanted to expect some gains from it. But some stablecoin can get some rewards by holding, if you know Binance and other cex there are option to stake, or earn APR just by locking your stabelcoins there but of course the profit is not comparable to other crypto like eth, and mostly defi tokens.