File History filled with .pst copies

My Outlook .pst file seems to be about 100MB.  And even when Outlook is not active, the file is touched about once every 30 minutes, causing File History to make another copy.  So my File History drive fills quickly.

In tasks, the only Office-related task I can see is "Microsoft Office Click-to-Run (SXS)".

Yes I know I can go to File History and make the relevant folder an exclusion.  But then I loose protection for that .pst file.

Is this a known problem?