First of all, if you don't know already, stETH is minted form staking ETH on Lido Finance protocol and can be used across Defi for various purposes like trading, farming, lending, etc. For Example, if you believe LIDO is in a good position to buy, and you have pile of ETH in your wallet, you don't have to buy LIDO with ETH. You can stake your ETH in Lido Finance and Swap your stETH for LIDO. You will be able to claim back your original ETH by burning equal amount of stETH.

As far as i know, there are not so many pools across Defi protocols for stETH, But some protocols make it possible to "Swap in and out" from stETH by swapping automatically for desired asset. for example, there is no DAI-stETH Pool per se, but this is a interface where smart contract swap your DAI to WETH and then uses WETH-stETH Pool to trade that for stETH. assuming this is true, Now is the time to take a look at most popular Pools and Tokens for stETH in Charts below:

I provide the tables in which you can see the exact amount and number of transactions for each pool