Testing another game, and due to the results, it looks like it is a particular game problem related since here the performance is way better than before with Medieval Dynasty.
Well, still try with ReShade it might hack that problem
But other than that - i’m afraid all you have to do in that case is just read comments on protondb, once it’s get fixed you’ll know
Or try each new Wine / Proton / GE / TKG engines versions until you find the one
I’ll try that ReShade technic and see what happens; at least we’re knowing who’s the culprit so far.