Since July 2020, my MacBook Pro (Escape key model) had been gradually losing drive space in significant amounts. It worsened in September, to the extent that I'd lost 20 GB of space somewhere. Detailed searches revealed the main Library had picked up cache files in the Application Support folder, I was unable to delete them.
I tried a couple of Time Machine restorations, to no avail. Still the excess was being stored. Apps such as Tech Tool Pro & Clean My Mac X showed the theoretical free space to be 140 GB but I could only access 118 GB of that. Desperation set in.
I cloned the Home folder to a folder on an external SSD then started the Mac in Recovery mode. From there I used Disk Utility to erase the Mac's APFS volumes and restored ti OS from the internet. Much downloading of apps & updates plus copying from other clones let me finish the process in about 18 hours, including sleep time. Then I had to re-enter the credentials for dozens of apps. This is made easier by the use of a password manager, I use 1Password.
I think it's all done, I have my free space back & the thing is running better & starting a lot quicker, too.