@nemo93 And here it is, a shortened (mostly rant free) summary of my last weeks experiences with dosbox-x and dosbox ECE with a slight taste of 3dfx gaming (for dosbox-x with compiled OpenGlide as a wrapper).
Building ECE is imho a real PITA compared to dosbox-x, but nevertheless...
Under retropie (terminal) i had to experience, that as soon as usescancodes is true, and apparently thats valid for internationel keyboards if set as such (I am on a german one), the keys are shifted by 8 (backspace is u, c is right shift, etc.) - to keep it short, I had to set scancodes to false and using the keymap I found in a german forum here: Raspbian und DOSBox - Tastatur (still had to swap yz in it, but it spared me the time of making one myself).
For a quick Glide test I used (an image) of my "Extreme Assault (GER)" Cd patched within dosbox* to xa_110 (the first patch added a 3dfx exe, before it was plain/mmx enhanced only) and well... being unable to use opengl in the (pure) retropie environment, 3dfx gaming on it was unbearable as dosbox-x used its internal glide-emulation (and music was only midi, the tracks from the .cue/.bin image weren't recognized). For dosboxECE it was a complete failure, as that one was complaining/aborting the start of xa_3dfx with a "Fatal error: unable to load DLL".
Ok, switching over to Raspberry OS (not sure whether needed or not, but with enabled experimental OpenGL set in raspi-config)... compiled both forks again... no german keyboard trouble, and at least i was able to play the first three missions with openglide in dosbox-x (here the mounted image played the cda tracks just fine)... wasn't that bad an experience, but in further runs... from time to time the gfx lost the textures and showed just polygons or major glitches. Dosbox ECE had the same problem as before "unable to load DLL".
So for now, I think to skip further Glide/Voodoo experiments on the raspberry and try it under Ubuntu and Windows (later one with the option of dgVoodoo and/or nGlide vs. Openglide could be the better option... if not, german keyboard again, dosbox-x would suffer from this unfinished issue AltGr issues when using MS-DOS which is, with my intend of running a W95B/W98SE in it, somewhat a nogo. Under Ubuntu there are no keyboard problems so far. And I haven't tried ECE in WIN/UBU so far. ... but those experiences are better to be told elsewhere.
P.S.: I really don't get it why under x11 environments the scancodes have to be shifted by 8, or why the sources assume that to be true if it is a *nix system.
Edit: The .dll problem with dosbox ece was that I had forgotten that I had replaced the glide2x.ovl in the game directory with the one from dosbox-x (for the openglide wrapper test) - but dosbox ece turned out to be unplayable slow too (retropie environment, raspberry os not tested yet)