I don't know what you think compacting is. But it is not what you are describing.

Compaction is the removal of dead and discarded data from the MBOX file Thunderbird uses to store mail, It is a housekeeping process where mail that is marked as deleted from the folder is not included in the data when the file contents is copied to a new file and the old one is deleted.

Occasionally there have been bugs in the compacting process, most recently in the 128 initial release See https://bugzilla.mozilla.org/show_bug.cgi?id=1903174. Compacting has never occurred on a timed basis at all but the rewrite that made it to V128 is discussed here https://bugzilla.mozilla.org/show_bug.cgi?id=1890448. I am not aware of any setting that might cause it is fire based on time. The automatic process is fired based on the amount of space in a folder that is occupied by the mail in the folder marked as deleted. The mail is actually removed instead of simply being hidden.

See https://support.mozilla.org/en-US/kb/compacting-folders and https://support.mozilla.org/en-US/kb/compacting-folders-potential-complications

So in other words, what you're saying is that all of my mail older than 30 days old is being deleted completely and no longer accessible or recoverable at all. Also, it only affects my inbox and not my trash mail or my spam either. Usually it's not exactly 30 days, so maybe it's approximate. (Maybe I just hit the storage limit every ~30 days.) I actually have compacting turned off, but it still happens. Also, for reference, I uploaded my disk & index settings.