Per VanguardLH:
If you don't need them anymore or right now, does disabling System
Restore help? You did not say what type of disk you have: HDD or SSD.
System Restore can cause heavy slowdown on SSDs.

HDD, but I will try disabling System Restore anyhow.

But that would still beg the question of "Why now and not
before?"....i.e. it would seem that something had to change to create
this situation between now and, say, four months ago when it did not
exist.

Not my PC, of course.... And the owner's husband is one of these users
that will say "Yes" or "OK" to anything that pops up.... which is what
got me thinking about the possible malware aspect.
--
Pete Cresswell