I just spun a container up to test this, it disables the registration and only allows invites after the initial account has been created, it returns an error if someone accesses the registration page and tries to create an account, https://www.focalboard.com/guide/server-setup/#registering-the-first-user
To invite a user, click on the Focalboard logo in the top left, Invite users, Copy link.
There doesn't appear to be anyway to manage users or non-owned boards, you can reset a user's password through commands, https://www.focalboard.com/guide/admin/#resetting-passwords
As an adult, we do too, and it also negatively impacts us. When I left the other social platforms I took the time to uninstall or disable many notifications, I now receive a total of 5 a day on average. It's good to see these conversations happening though, whether we react and change though only time will tell.