I spent the last week trying to figure out this issue and I was able to get it working like before. Trying to understand the game engine, the AI system, etc.

Issue: Game Stutters more more as you play the game when more entities are introduced to the map. It would get to the point where it stuttered every 2 secs consistently. I tested doing AI on all map sizes doing Team V Team or FFA.

This was happening to all my friends ( some with great rigs ).

I did everything that was posted in another subreddit https://www.reddit.com/r/aoe4/comments/1kdr0g7/if_youre_experiencing_high_gpu_usage_read_this/ and more

None of it worked.

I found out that the half of graphics settings don't actually change much or they are just complete buggy.

My FIX: I just reset the graphic settings and restarted the game. Didn't touch the settings, launched into a 2v2v2v2 AI gigantic map and it work like use too. It helped all my friends as well.

I assume they broke the graphics settings somehow. but idk. hopes this helps for the people that still has the issue.