I see you're using MangoHud. Does your frametime graph look flat, or is it going haywire? In my case, I had games running around 120fps, but displaying at a rate that felt below 30. This was the case until I ran games with MANGOHUD_CONFIG="vsync=3". Could be worth a shot.

You could also access it via ADB, and Shizuku lets you access ADB permissions on the device itself. No root required either, but the app needs to be built to use it. I found this file manager to work pretty well.