Which uniswap address holds the liquidity pools tokens?

Hey there, my project requires that I know how many of the contracts tokens are in the Uniswap liquidity pool, so I can deduct them while calling:
function totalSellableSupply()
tokenSupply - tokenBalance(whereuniswapkeepsthetokens)
I'm not sure which address would be responsible for telling me this. Any help is appreciated.

:1234: Code to reproduce

:computer: Environment

It's probably impossible to retrieve how many tokens are locked in Uniswap overall.

In Uniswap V2 you should be able to check how many tokens are locked in a specific pair, by using getPair and then getReserves.

I can't find how to do this in Uniswap V3.