Please confirm you: Emptied the Trash Emptied the Junk and then compacted the Junk folder Compacted all other folders including the Drafts. (right click on folder and select 'compact')

Yes, trash emptied, files compacted. The Trash has developed a problem, after something is sent to Trash the first time, when something else is sent to Trash, the "spinning circle" starts and does not quit, and the message is - There is not enough disk space to download new messages. Try deleting old mail, emptying the Trash folder, and compacting your mail folders, and then try again. - I do that, but the only way to use the Trash after that is to close Thunderbird and reopen Thunderbird. I want to move my Thunderbird to a new computer without including old emails that have been trashed. The size of the Profile folder and 566jlfn3.default folder indicate that there are more files that I see in Thunderbird. When I downloaded the Thunderbird program to my new computer, that folder within the Profile folder has a different name than the 566jlfn3.default folder. I never noticed that before, and I have transferred my Thunderbird Profile folder to new computers 2 or 3 times before.

Is 10gb the size you expect, or something less? And what does the mail server report as being used?

We backed up the Profiles folder and archived it. We then deleted emails prior to a certain date. The Profiles folder is not smaller than 10 gb with about 37,000 emails saved. However, the program has lost emails within a time gap for the last quarter of 2020. Even if we reload the Profile saved in January 2021, those emails cannot be found. Now, if the Trash is emptied, nothing can be put in the Trash unless the program is completely closed and reopened. We can accept the fact that our efforts to reduce the size of the Profiles file may have accidentally resulted in deleting or losing files for the last quarter of 2020. We would like to fix the Trash issue.