I have to put this mod here, even though it could be scary.
When you have many mods in the most recent version of Minecraft, but the server that you're trying to connect to isn't compatible with your version, Multiconnect tries to make your client act like an older version of the game to the server.
Notice: This isn't really necessary for most popular servers (Hypixel) since they run the compatibility on their end, but the server's implementation is not perfect (they can't stop players from 1.13 swimming, while this mod can).
However, if an error happens with this mod, the server might see you as passing illegal/ hacked data, and will have a reason to ban you instantly. I have this mod uninstalled for this very reason (I'm afraid of Hypixel), but if you're sure that the server won't kill you (a friend's older server, or the sub server before it updated to 1.19), then having this mod in your radar could save you a LOT of hassle.
https://modrinth.com/mod/multiconnect