Sway? Cosmic? OpenBox? KDE? Like, look up some DEs, look up themes on Pling, and pick your favorite. Try them out in a VM.
Cinnamon has made opinionated choices based on the majority of their demographic (newbie users). If you aren’t a fan, pick something else.
So, genuine question: why btrfs instead of zfs? Sounds like your use case would fit the latter.