This was a known issue with Chromium on Wayland with high-DPI displays at one point
https://github.com/RPi-Distro/chromium/issues/40
https://www.reddit.com/r/kde/comments/167lkln/chromium_doesnt_respect_cursor_settings/
I'm not sure if you're under Wayland, but that second link suggests setting the cursor-theme in ~/.icons/default/index.theme too:
https://www.reddit.com/r/kde/comments/167lkln/chromium_doesnt_respect_cursor_settings/jys1rsh/
