for lutris just use winetricks for right prefix, you need both dotnet452 and xna40
try wineGE or wine-tkg, proton is just for steam
32bit, 64bit, i don't know, for me it never mattered. launching underrail via steam/proton always worked flawlessly. it could be your old hardware, or maybe you selected wrong driver(maybe mint issue), so u 'now, maybe, maybe, maybe
lutris should be able launch gog games, no problem, underrail included. try again, or switch to heroic launcher