Well, you have to specifically ask for a 32-bit Win10, so I'll assume you are running 64-bit versions of your OSes. That only leaves checking the SH4.exe to be sure it is not set to "Read-only" in its attributes, so that a LAA applet "takes" on the SH4.exe file. Another thing is if you are still using the same SH4 Save folder information (usually "C:\Users \UserName \Documents \SH4"), then you might empty that to clear the old contents out. The game runs off of the info in that folder. It will also re-set your Options settings in all of those menu choice areas, including sound, game options and graphic options, so you'll have to go back in to put them how you want them. You also, of course, lose all game progress, so if you're just wanting to experiment with re-doing that, instead of deleting the info, copying and / or moving it to another folder to keep it safe might be a better way, so that you could restore that if new data fails to help.
After that, if you followed all of THEBERBSTER's info, and you don't "shell-out" to the Windows desktop, then I'm at a loss. SH4 has fewer issues with graphics than SH3, and when you do have issues, it is usually easier to deal with... perhaps it is hardware with either the vid card or the display, but I don't see how. As stated before, the game has a tendency toward looking like that with dead-calm seas, and usually, most mods with a different scene.dat file do help...
