if you have btrfs as the filesystem, try filesystem compression. if you have stuff which can benefit from compression, it can reduce disk usage significantly.

if you format a new partition, add compression as a mount flag (zstd, level 3).

if you already have a system without compression, do something like

sudo btrfs filesystem defragment -r -v -czstd "path_to_file_or_folder"  

do check properly in btrfs docs (this command is not that unsafe, but any file system operation has some inherent risk, so please do it carefully).

you trade disk read speeds and slight cpu usage (less than 1-2%), but if you do not have something that io speed dependent, it is great. (imagine things like game folders, or root /usr dir which has packages)