Theme admin page not working

I can't reproduce this on a fresh install. Please provide the steps how you installed the theme and what Drupal version you're on.

Drupal Version is: 10.4.6 with a fresh installation where I did a data migration from an old drupal 7 site

Looks like you haven't set Gin as the (default) admin theme

Maybe try to follow the steps in https://www.drupal.org/docs/contributed-themes/gin-admin-theme/installat... →

if it doesn't work try to simply uninstall and install it again (maybe the hooks haven't been run)

Cheers

Just saw that there are console errors