Where has the network-manager service in 21.10 gone?
Solution 1:
The NetworkManager service has been named NetworkManager for a while now, and network-manager service was kept around as a backwards-compatibility option (see What's the difference between network-manager.service and NetworkManager.service in Systemd?). It looks like that was finally dropped in Ubuntu 20.10 (Groovy Gorilla), and now only the NetworkManager name remains. You can use it like so:
sudo service NetworkManager start|stop|...
sudo systemctl start|stop|... NetworkManager
sudo systemctl start|stop|... NetworkManager.service