The Raspberry Pi Imager works fine. You start the app. You choose the image in the first menu, you choose the sd card (or an usb stick, an usb ssd or an usb hdd) in the second menu and then you click on the button "write". The app downloads the MoodleBox 4.5.0 from the internet and copies the image to the sd card. I tested this with an usb stick with 32 GB.
Starting the MoodleBox works as usual. Put in the sd card or the usb stick into the Raspberry Pi. Switch the power on and wait a moment. Connect to the MoodleBox wifi and open the page http://moodlebox.home/ . The moodleadmin is the user moodlebox as normal.
To connect via ssh you need to use a monitor and a keyboard at you Raspberry Pi. You must add the admin user. No, there is no admin user moodlebox when you use the Raspberry Pi Imager to install the MoodleBox. You can use any username you want. But remember ... the documentation on https://moodlebox.net/ shows everything for an admin user moodlebox. When you added the admin user then log in. Start the rpi-config program and activate the ssh connection.
No, I can't preset any option in a settings menu. There is no settings menu when choosing the MoodleBox image ... I tested this on Linux and on macOS. Something is different to the standard Raspberry Pi OS image. Choosing Raspberry Pi OS I get an additional settings menu where I can set the admin user and activate the ssh connection.