Try Glary Utilities, free download.
In 2022, I had a similar problem and Glary found it.
Go to the disk space analyzer and see what’s eating your disk. The problem was the System Volume Information folder that was filling up for no apparent reason with dozens of files each occupying 5-8 gb. I found a way to limit that process, though I forget the details, and haven’t had a problem since.
I was so happy with what happened, I signed up as a paying customer.
I highly recommend Glary.
Now I remember, I limited the size of the System Volume Information folder, which still allowed new files to be stored and older ones to be deleted, which wasn’t happening before.