>Often software that is 20 years old will not require this.

A quick search around the net reveals this to be false, because Windows XP Mode doesn't work in windows 10. I haven't used windows in many years so you'll have to forgive me if there's something I'm missing here, but I see quite a few pages like this complaining about XP programs being broken or requiring a lot of fiddling to get working: https://www.dosgamers.com/windows-xp/windows-xp-games

It makes no sense to me that you have no problem with this, but at the same time you're complaining about having to type something like "docker run ubuntu:precise" to get an old version of a Linux userspace running inside a container. If this is too much work then you can pay Canonical or Red Hat or any of the other numerous Linux companies for a support contract for an LTS distro. This seems to be very similar to the situation in redmond where you now have to pay for an extended support contract if you realistically want to keep using Windows XP/7.

This is my point: sometimes 20 year old Windows software doesn't work. What you're seeing is evidence that it is the exception rather than the rule because people expect it to work because it usually does.

In the Linux world, the community is pretty actively hostile to people simply wanting to run software not in the repo let alone originally compiled 20 years ago.

I don't see any evidence to support the assertion that this is the exception rather than the rule. My searching has only shown evidence to the contrary, that various fiddling and workarounds need to be done to get old apps working properly in Windows 10. Even moreso if you want to use some of the newer features they're promoting, like tablet mode or high-DPI. Legacy apps just don't magically work in those situations. Here is another source for this directly from MS, where various workarounds are suggested: https://support.microsoft.com/en-us/help/3025083. Again I am not a windows user and I'm just going off of web searches so if you have some other evidence then please tell me. I just simply do not believe that MS has some kind of magical solution for perfect backwards compatibility. Supporting that stuff continues to take up engineering time and they will also gladly charge you an arm and a leg if you insist on needing it.

>In the Linux world, the community is pretty actively hostile to people simply wanting to run software not in the repo

This is wrong. Supporting software that is not in the repo has been the primary reason for adoption of containers, and also other similar things like flatpak and snap. The only difference with these is that the upstream distro cannot possibly support them because it goes outside their scope, so you have to get support from somewhere else.