Hi JanB,
I received your PM. So glad to hear things are active here!
The reason we were able to fix SFC2 was because we had the source code to fix it. The problems were not something a 'compatibility mode' could fix. There changes needed to the actual code itself.
In the case of SFC3- I'm sorry to say I've never played it. I was not aware SFC3 didn't work on Windows 8. From your description, it is not exactly the same compatibility problem as we had with the original SFC2. As far as I can remember, it didn't have graphics problems like that.. But my memory is very old... So what I'm saying is, I can't exactly comment on what you are seeing, although it sounds like you already did some homework.
What I can contribute is.. During working on CE, I did see a similar problem to what you describe while working on code. As a tiny background, the code we received was not exactly like what SFC 2 was in last release. The code for SFC2 we were given had sections of newer 'never before seen' code and original code. In what we had been given there was a section for this version of SFC2 to use the same graphics sub-system as SFC3. It didn't work out of the box, and revealed itself as a black screen but visible mouse, etc, similar to what you describe. My fix was to rewrite the affected section to NOT use the SFC3 graphics subsystem, and connect to DirectX in Windows directly, which was how the original SFC2 was written. But you can tell something else from all this... In SFC 3.. The mouse.. it renders directly to Windows... the rest of the screen.. it renders through its own graphics library.
Now, I don't say I know whats wrong with SFC3, because I haven't played it. But I know a tiny bit about how it connects to Windows to display graphics. Based on what I had experienced before, I would say its showing that same old thing. Where the game connects directly to Windows DirectX, it is able to work (mouse), but where it attempts to use its own graphics library (the user inferface) it fails. I would suppose the problem lies in the code of SFC 3's graphics library.
And unfortunately, we don't have the code for SFC3. So we can't rewrite it. And as to what changed in Windows as to why Win 8 doesn't like it anymore.. I don't know, I'm sorry.
If I was really dedicated too all this.. There might be clues to make a new graphics library for SFC3. Recall that the code we were given had incomplete pieces of it? Well that could give clues to just make a new one and replace the library SFC3 uses... Buts that's a lot of work...
I'm sorry I'm not more helpful.. When it came to SFC2, no compatibility mode ever fixed our problems. They were not fixed until we got source code. It may be that SFC3 succumbs to the same fate.