Wrong link to Drupal's permissions page
CiviCRM 5.31 on Drupal 8 has in the web UI at
/civicrm/admin/access?reset=1 a link called Drupal8 Access Control, but it is leading to
/civicrm/admin/access?reset=1 instead of
/admin/people/permissions, i.e. not where it should.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information