Due to a minor error with file system permissions in the latest release (v20.12), the FreedomBox process fails to start.
A patch fix release v20.12.1 will be made soon. Your FreedomBox should automatically update itself in less than a week. The web interface will be available as soon as the update is applied.
Thanks to @kopfkind for identifying and posting the issue and solution on our forum.
Link to thread on the forum:
https://discuss.freedombox.org/t/fb-20-12-solved-plinth-fails-to-start-due-to-new-frontpage-py-shortcuts-and-filesystem-permissions/994