False insufficient-disk-space alert
Solution 1:
There are probably local snapshots on the data partition which is not accounted for in About My Mac > Storage. Use df -h or diskutil apfs list to view the actual disk space.
To list all Time Machine local snapshots, use tmutil listlocalsnapshots / or diskutil apfs snapshots / (much slower).
This command will delete all snapshots (in most cases):
tmutil thinlocalsnapshots / 9999999999999 4