https://www.reddit.com/r/NixOS/comments/1li2ypb/cursor_appears_double_gnome/
=> 504239 – Duplicate cursor appears after mouse is idle for a couple seconds, with single display or if multiple monitors using different resolutions are connected; display is set to Prefer color accuracy or with refresh rate > 120Hz
==> https://gitlab.freedesktop.org/drm/amd/-/issues/4307
from the bugs discussions it looks like amd related issue
try different kernel versions either later version (assuming it’s fixed) or earlier (if not fixed yet)