All new Plesk Obsidian servers have this feature enabled by default, while on upgraded servers this it should be enabled via a command-line interface with the command.
Use either of the following commands:
# plesk bin admin --enable-access-domain "server.example.com"
In this case, if there is a website with the specified name, it will become inaccessible because Plesk panel will be shown.
# plesk bin admin --enable-access-domain ""
In this case, panel will be accessible on any domain hosted on Plesk and not having website.