With the latest version 27.0.0 of NextCloud at the time of writing this article, the group add feature from the admin WebUI is broken (adding a group and press the save button does nothing).
This is a known bug and should be fixed in version 27.0.1 which should be pubished in the next week(s).
In the meantime, you can use the “occ” command line utility to add groups. Here are the possible related command groups :
group group:add add a group group:delete remove a group group:adduser add a user to a group group:removeuser remove a user from a group group:list list configured groups
The full command to add a group would look like this :
sudo -u www-data php occ group:add NewGroup
Note : The example above assume that your Web server is running as “www-data” user.
Even though this issue does not prevent users to be added to an existing group from the admin WebUI, you can also use OCC to add a user to this new group as followed :
sudo -u www-data php occ group:adduser NewGroup UserToAdd