That’s the problem though, your scenario is making a boat load of assumptions to stand up a theoretical point. Assumptions that the user is running a specific distro, that they then want a specific application and that application has been unmaintained for more than 10 years. This isn’t a common scenario regular Linux folk are going to find themselves in.
Plus the situation wouldn’t be any better on Windows (good luck finding the installer for software that has been abandoned 10 years ago from safe places online) nor macOS (Apple do breaking changes more frequently more than any other platform) either. And that’s without factoring in any security concerns that running software as old as that might introduce.
So regardless of the platform, if it’s consumer software (ie not industrial applications or other such specialist edge case), you’d recommend the user switches to a newer and maintained alternative.
"your scenario is making a boat load of assumptions to stand up a theoretical point"
Well, that's the scenario the original post made, not mine. From my experience, this can happen albeit rarely - especially with closed source software.
"specific distro" == The most popular Linux distros don't include old frameworks.
"they then want a specific application and that application has been unmaintained for more than 10 years"
This (for example) eventually describes pretty much 99% of games released natively for Linux, unless one goes with Steam which tries to keep stuff working (I dunno whether GoG or itch also do it).
For really old software, Windows is the best bet. Even if Windows itself doesn't work (it usually does), wine might.
Plus the situation wouldn’t be any better on Windows (good luck finding the installer for software that has been abandoned 10 years ago from safe places online) nor macOS (Apple do breaking changes more frequently more than any other platform) either. And that’s without factoring in any security concerns that running software as old as that might introduce.
So regardless of the platform, if it’s consumer software (ie not industrial applications or other such specialist edge case), you’d recommend the user switches to a newer and maintained alternative.