I started with ~30 gigs on my machine. After trying all of the solutions posted here, I ended up having to first purge my drive of unused applications (mostly pre-installed applications ) which got me to ~40 gigs. The update still didn't work. I then uninstalled and reinstalled Xcode to get the latest version (Xcode 12). I only have 3 non built-in applications installed and a few code bases that I use to develop all under ~10 gigs total. It feels like Apple just wants you to buy their iCloud storage out of frustration.