High video memory consumption when displaying background images
radeontop, GNOME (in Wayland session, one 4k screen, with a single terminal window running) uses 584M of VRAM when displaying
/usr/share/backgrounds/gnome/Fabric.jpg image as a wallpaper (168M when displaying no background image). In Xorg session, these numbers are even higher, 655M and 238M respectively.
For comparison, Sway uses 140M, Openbox+feh 145M, when displaying the same image as a wallpaper.
Here, a Reddit user complains about stuttering in a video game caused by high VRAM usage in GNOME. I believe this might be one of the culprits.