When using rpi-imager to prepare an sd-card with Ubuntu Server it is not clear how to finalize the setup.
After some triall'n'error I found the following.
Boot the image and wait a few minutes until the system settles - the green led is an excellent indicator.
When the system has settled either attach a monitor and keyboard or use nmap to locate the device
nmap -p 22 --open ip.x.y.z/24The default login is ubuntu:ubuntu - you will immediately be required to change password, follow the prompts.