It is difficult to suggest anything - as it is not my system.
Cleanup the journal
journalctl --vaccum-size=50M
Cleanup your pacman cache
sudo paccache -ruk0
Cleanup your Trash
rm -rf ~/.local/share/Trash
Flatpaks and snaps can easily take up space - a lot of space
I don’t know anything about snaps but located some 3rd party info
sudo snap list
sudo snap remove <pkg-name>