Chrisjmj's post was evidently above my (admittedly low) computer skills! The first time I tried it, nothing happened, hence the "Wait for what?" comment in the previous message. The second time generated only error messages. The third time generated error
messages, but still ran for long minutes (sorry, I didn't time it) and kept showing lines like "such-and-such app ... 100% complete".
The fourth time, I entered the (Get-AppXPackage...) command string manually so that it eliminated the ">>>" symbols generated by my cut and paste. THIS TIME, it ran without any errors, and only took seconds (I think the third time did actually repair some
stuff).
Alas, it was good news/bad news for me. The Solitaire Collection has reappeared on my start menu, but still will not stay open (opens and then closes within seconds.)
Good news, the Alarms & Clock app is now working for me. (It was closing immediately after opening.)
Bad news, the Photos app is still closing immediately after opening.
This repair was certainly worth a try, and might fix the problem on your PC!