It’s already been explained elsewhere, but the cache can be free, as needed - that’s how linux works.
There’s 57+ GB available ram, yet.

every chat app might use ~1GB because most of them are electron apps, which all spawn their own instance of chromium

I was running mint with 4gb with steam and signal on background as well as Firefox with 2 tabs open. Not perfect but definitely usable

Hey, unused memory is wasted memory