So I can already tell this has to be cache because I did download a 20gb modpack but after cleaning out my cache (At least id think so) its still taking up 20gb

Will it go away eventually? I dont need the space immediately but im really confused why this is happening.

where can you find stored auto fills, what I mean by this is where can you find the stored data for the drop down menu that you'd usually get for emails or usernames.