The limitation isn’t really arbitrary once you put a processor in in long mode (64 bit) it can’t do Virtual 8086 Mode any more. One of those things AMD did when designing 64-bit mode to clean up that particular can of hysterical raisins.
…also, even back in the days processors were fast enough to run that old stuff under DOSEMU. Which you probably want to do anyway as you don’t have a Roland MT-32.
Oh, EDIT: I had once fullscreen issues under wine, and that was Witcher 3, not the current upgrade the older one: Alt-tabbing away worked perfectly, but the game didn’t properly recognise that it had lost and re-gained focus, refusing to go out of pause. Switching fullscreen mode in-game (fullscreen to borderless or the other way around) fixed that.
Wayland is way better with fullscreen than x11, btw, especially considering that there’s still the occasional SDL1 game around, those will right-out switch your video mode and disable alt+tab.