I think the interface breaking on newer screens is a key point - AOE2 definite edition looks great on a 4k screen now, but when I tried one of the other variants beforehand the UI didn't scale properly and so all the elements were tiny to the point of being unplayable without adjusting the resolution

I play lots of old games, but the thing I have the hardest time with is playing in 4:3 on a 16:9 monitor. I didn't6 know why... Maybe I need to try an actual 4:3 monitor and see how I feel.

Have you tried 0ad by any chance?