Changing game settings has no effect on performance

Hey there,

Do you have Geforce Experience optimizing the game settings by chance?

Maybe there is some external program like that which is overriding the in-game settings.

The game reads/writes the graphics settings to Settings.json in this location:
C:\Users(your username)\Saved Games\Diablo II Resurrected

You can open with Settings.json with Notepad. Maybe try changing the settings in-game and just verify the settings are actually changing in that file. For example as a quick test you could try switching to Windowed mode and chose a lower resolution in-game, then close the game and inspect that file to verify if it actually saved properly.