I just did a fresh install of Ubuntu Server 20.10 64 bit on an RPI 4, and it connected to the Wifi on first boot, so it might be OK to remove the line about needing to reboot?
I suggest simply looking up the IP addresses in your routers DHCP table. The arp command didnt show my pi neither on LAN nor in WLAN.
Moved from the Pi Tutorial thread into a new thread for support.
Documentation threads are for specific feedback ("Change X to Y; Z changed in 20.04)"
Please don’t use documentation threads for support and help requests.
The best place to ask for help is in one of the Ubuntu community support sites. discourse.ubuntu.com is not intended for support.