(1) "I think PCR didn't really know yet that an in-place upgrade can't solve some problems that a system image restore can. Nonetheless PCR's suggestion to make system image backups is good. We can conjecture now that a system image restore might be able to solve some problems that an in-place upgrade can't solve, though I don't want to revert my Outlook PST files and Firefox session history to earlier dates."
I did know that an image restore could out-do an in-place upgrade which may or may not fix a problem.
An image restore gets the computer back to where it was before the problem surfaced. If the problem didn't exit before the image was made, it shouldn't after it is restored. But hardware won't be fixed. If credentials (or something like
that) had changed after the image was made, you'll have to change them again.
And - you are right, good catch - databases held in a partition that is restored will revert to the date the image was made. Also, mounting the image for individual files will suffer the considerations you said. In addition, if you have set OneDrive
to "Files On-Demand" for your user files & hadn't downloaded the files, they won't be in the image.
An image restore probably wouldn't link your computer to your Microsoft Account (that depends on an entry at the site) - but it should be a repair for the Store. Then, when you open it, it probably re-links. That's my theory.
An in-place upgrade seeks to keep settings. So, if settings is at fault, that won't get fixed. It too won't sign into your Microsoft Account & link the computer to it, I don't think. If the problem has to do with a 3rd-party driver or executable,
that probably wouldn't be fixed. I would expect it to repair the Microsoft Store - it's a sin it didn't.
(2) "No, just now I reset the Calculator, but it still doesn't run. Also there's no option to repair the Calculator. There's an option to uninstall the Calculator, and I don't know if that will work when the Store isn't working, but without the Store I won't be able to reinstall the Calculator."
(a) The Calculator & the Store can be downloaded from the NET too. But I'm unsure that's the way to go. So far I've seen only older versions. I'd like to see one that says it's for Windows 10.
(b) Why don't you create a Microsoft Account on that computer? It will link them. Then, just wait a bit to see whether the Store will self-correct. Monitor "9WZDNCRFJBMP-MICROSOFT.WINDOWSSTORE" in Reliability History
to see whether it will come in good & be a fix. Afterwards, you can try to unlink the computer, if that's what you want. Hopefully, the link to the Store will remain.