I had this issue with the latest RPIOS using Chromium 133. Our Chromium is currently at 131 so it is possible that once Manjaro reaches version 133 or higher, this problem will also manifest for us.
The issue is that Chromium started to switch the “vsync” on when you go fullscreen (F11). This is a newly introduced behavior. In powerful machines with good gpus, this probably wouldn’t affect the performance. For low powered machines like our raspberry pis, this causes a huge frame drop in 3d content and videos in web pages. Even youtube suffers greatly.
To remedy this, we need to disable the vsync by adding the following flag to the “chromium-flags.conf” file in our $username/home/.config directory.
--disable-gpu-vsync
That is all.