I just resurrected a 90s kids CD-ROM game that shipped for Windows 3.1 - https://github.com/matthewbloch/orlys-draw-a-story-fixes

The finished patch DLL ended up being a tour of the stuff that broke.

The game did launch on Windows 11 but the main issue was that the 8-bit pre-DirectDraw behaviour was broken - for 256 colour screens, Windows 11 resolvesld palette indices only once, but the game relies on being able to change the palette for fades etc. Most of the screeen ended up black, but you could see the animated parts just fine.

So most of fix ended up being to hook every draw call and implement a virtual GDI that acted like a graphics card of the day.

There was a 32-bit disc space check that overflowed, a couple of use-after-free crashes and some racey threading calls that can't have been tested on a machine with 2 CPUs.

Backwards compatibility from Microsoft was almost all there, and probably would have kept Orly running for a couple of subsequent Windows releases. But it relies on a developer meeting them half-way, it's not an emulation layer.