Keep in mind that software doesn’t have an expiry date. If a piece of software is unmaintained and doesn’t have an active fork but it still fulfills your use case and doesn’t have any major issues, there’s no need to replace it. Some of the software I use hasn’t seen any updates in five years but I still use it because it still works.
Edit: As an example, a lot of people still use WinDirStat even though the latest release 1.1.2 is now 17 years old.
Desktop - Linux - Yes, likely. If not, here’s a flatpak
Desktop - Windows - Maybe it still runs in a compatibility mode?
Desktop - iMac - Here’s an emulator, good luck.
Mobile - PostMarketOS - Yes, likely. If not, here’s a flatpak
Mobile - Android - Maybe? Try it and see if you get permission denial
Mobile - iPhone - Fuck you, no.
Windows is pretty good with backwards compatibility, probably the best out of anything. I can run Visual Basic apps I wrote in the early 2000s on Windows 11 and they still run fine. Some old 32-bit games work fine too. You can even run some 16-bit Windows 3.0 apps on 32-bit Windows 10 if you manually install NTVDM through the Windows features (it was never ported to 64-bit though)
Linux is okay for backcompat but I’m not sure an app I compiled 20 years ago would still run today.