Looks like the artifact of buffer color depth/size mismatch. Have you tried it with dgVoodoo or DXGL's replacement ddraw.dlls?
Doom95's generally ick because of the Win9x-centric mouse support, but that's besides the point 😀 I get what you're trying to do, play the release as it were on a platform unforeseen. though to be fair XP wasn't on the agenda when Doom95 was developed up at wildtangent in 95. They had to do something to desperately show off DirectX with something well known, and with that desperation came the need for speed, and with that need for speed comes that obviously small pixel buffer being handled by 10 improperly.
it also shows that zenimax must get off their ass and do something about the Steam doom releases after Windows 10 launches because it WILL be like this, and there will be a lot of tears.
by the way, DOSBox is not for running Windows 9x