If the issue were bit depth alone, then using an XP VM on a 64-bit system wouldn't work, either.
Bit depth is not likely the central issue here. There are many reasons why certain old software may not work on Windows 10, but it is "certain old software" as there's quite a bit that works just fine. And most of what works just fine is 32-bit software running on 64-bit machines using 64-bit Windows 10.