If you’re running a Mac with limited internal disk you’ll encounter this message: Your disk is almost full

There’s a great article on how to manually delete Time Machine Snapshots

Key steps:

  1. List available local snapshots “sudo tmutil listlocalsnapshots /Volumes/Macintosh HD”
  2. Delete each snapshot “sudo tmutil deletelocalsnapshots 2020-11-01-002004”

I’ve had to do this a lot when upgrading to a new beta release.