New Mini M4, cannot get past login screen

I bought a new Mac Mini M4 (the base model) a couple of weeks ago. As soon as it arrived I plugged it in and started going through the initial setup, but before I'd logged in with my Apple ID I got distracted by something and ended up shutting off the computer and not coming back to it until today. Now when I turn it on I'm greeted by a login screen asking for a password, even though I haven't yet set any password or previously logged in, and can't find a way to get back to the set-up I had started working through a couple of weeks ago. There doesn't seem to be any option to even enter a username! What should I do?