Created an MS account (because I want this machine to be as normal-user as possible), set up a PIN. Signed in with a PIN to the desktop, run 'Remote desktop settings' and fip the 'Remote Desktop' toggle to on and affirm the prompt that asks if you really want to do this.
After that no issue RDPing to the machine by IP or hostname from another machine on the same LAN. Username and password is the same as the MS account I first signed in with.
(For reference, Windows 11 22H2 running on an HP Prodesk 600 G5, RDPing from macOS using Microsoft Remote Desktop 10.7.10 installed via App Store.)
But yeah, I'm pretty sure the domain join is only an option on the pro and enterprise editions.
I've also found out that the domain join is only offered if it can contact the internet. I installed this on a brand-new laptop the other day, and it didn't detect the wifi card and it had no wired network. It absolutely refused to go past the "let me connect to the internet" phase until I went through the "hidden terminal" dance.
This is in a stark contrast with current linux desktop distributions, which do allow domain join straight from their OOBE.