I have had a similar experience after i shared my MacBook with my girlfriend for a while. Turned out even after uninstalling her cloud file sharing software thing, there were still over 100GB of cached files left on disk. MacOS didn't make the obvious identify or find in the storage overview.

I ended up finding it through a disk space visualizer that showed a large folder (the stolen 100GB) in some cache directory. I can highly recommend trying that out. MacOS' inbuilt tools are in my experience inadequate to find what is stealing your disk space (on top of applications being unable to clean up after themselves).