"Previous versions" of text files (*.txt)

The Windows Back Up app (shouldn't that be Windows Backup? - no space?) just seems a first attempt to partially provide a single point to access built-in features. MS has failed (in my view and as stated in some articles I've seen reviewing it). Like Edge, I leave it well alone.. removing things that MS supplies with the O/S may give rise to trouble e.g. updates that don't complete...

Are txt files the only 'text' or Office file type that have previous versions?

And is that confined to those in Documents and not elsewhere?

And do all txt files have previous versions or only those older that a certain date?

I.e. is there any pattern to this?

For completeness, are you using OneDrive - or did you then? (Although I doubt that would be responsible for this... but I have no proof).

I thought Onedrive wasn't available to "local user" accounts?

True, but we are thinking back to - was it 2018?- when your account might have been different..

Good observation about System Restore, though I don't understand why it is related to this.
Once upon a time it was possible to modify the list of file types it addressed, but that is history.

I wonder if somehow the correlation is to do with shadow copies, and that somehow disabling System Restore affects shadow storage, and so affects your previous versions.

FWIW I'm reminded of
ShadowExplorer.com - About
which I've not used, but should let you view your shadow storage. Don't see how doing that helps understand what's happening though.

Question is, what's using shadow storage in such a way as to create 'previous versions' of files.

Researching Shadow Storage, shadow copies, might provide a clue- maybe you have some kind of backup tool or script - or had such- that does this.

Unleashing the Secrets of Windows Shadow Copy: Data Recovery and Beyond | by Adarsh Pandey | Medium
Onyx Boox Poke 5 Review: Good Enough to Bookmark
Shadow Copy - Wikipedia
How to enable Previous Versions to recover files on Windows 10 - Pureinfotech
etc

Here's a guess:
Assuming you're using (or have used) some form of backup program... and taking this as an example:


from
How to Use Volume Shadow Copy in Windows 10 Correctly

Note the VSS (Volume Shadow Copy Service) option.

Something that is running on your PC either did or does trigger or make use of VSS to back up the files for which you are seeing previous versions.

Note for interest that Windows Server has a context option to enable VSS backups for shared folders.. this is not available on non-server editions.