I am the owner of an SP online site and the permissions tab has been disabled for me.
Url of the above page is:
but I can still add users to the documnet library through the right-hand side menu as shown below:
I do not know how this has happened or how to fix the issue.
It seems that I can manage the groups in SP designer 2013 as well
Can it be due to ShortPoint SPFx? it seems I cannot remove it as there is no remove button for it: