I have just apparently discovered a workaround! (Thanks to @chrullrich whose comment gave me the hint.) Maybe it's been obvious to everybody this whole time but I have only now found out that when I delete the file %APPDATA%\Microsoft\HTML Help\hh.dat (in my case c:\Users\dvorak\AppData\Roaming\Microsoft\HTML Help\hh.dat), the problem seems to go away. I'm so happy I just had to share. :)

I also have another, possibly naive idea. While Microsoft has ignored this issue for years, they have recently "helped the community release their distribution of Python to the Microsoft Store" (https://devblogs.microsoft.com/python/python-in-the-windows-10-may-2019-update/), and by "they", apparently I mean the very same Steve Dower who comments here, as I just realized. :-D (So... thanks, Steve.) So I'm thinking, as we actually have a Microsoft insider here, wouldn't it be possible to make Microsoft fix the viewer so that it, I don't know, possibly DOESN'T CRASH? I assume that Microsoft has plenty of those crash reports in some database?