It’s not possible to register new accounts at Home · Wiki · F-Droid / wiki · GitLab, instead https://f-droid.org/wiki/page/Main_Page says
‘‘You can use your existing F-Droid credentials to log in here. To edit the wiki, however, you will need to confirm your ‘’‘email address’’’ via your [[Special:Preferences|Preferences]] (OpenID users may have to specify it in their [https://f-droid.org/wp-admin/profile.php profile] first).‘’
However, I cannot login with my forum.f-droid.org account (I’ve tried both the email and the user name, with correct password). I cannot login with my GitLab account either.