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.