Yes, I've seen this on Windows 10 Pro since 1803. Hilariously, it fails to open PDF's on an SMB share, says the file can't be found while listing its path. And the Microsoft Store is still so shady that I don't trust installing anything from a non-recognized vendor, so I ended up going to Adobe's web site to get Acrobat Reader which can open PDFs whether local or on that same SMB share.

It's because "Feature Updates" are actually in-place OS upgrades. They're essentially reinstalling Windows and migrating applications and settings, but also choosing to not migrate some of them.

Is that true? Does that mean that applications with a more complex setup will break with every feature update?

I would be okay with that if the previous setting is Acrobat Reader.

Perhaps you would - but somebody else's form filling just stopped working. Hey, no big deal: MS knows better than the user "where do you want to go today."