Does anyone know why DX8 games worked properly on 8, but not on 10?
"Because Windows 10". As someone who also plays a lot of older games, W7 to W10 has been a far bigger PITA than XP to W7 ever was to the extent I couldn't be bothered with all the extra hoops and
downgraded "re-upgraded" back to W7. Eg, No One Lives Forever wouldn't run full-screen. Forcing it gave a new weird 30fps cap that never existed before. Disabling it gave chronic tearing and weird movement stutter (due to VSync not working). The workaround which consisted of borderless window + frame-rate cap in MSI Afterburner, "technically worked", but despite supposedly running at a solid 60fps, it never actually felt as smooth as W7 full-screen. And that was the pre Anniversary Edition which from what I've heard is causing even more problems, even for newer games. Good luck if you can get it to work.