Genuine W11 iso, downloaded directly from MS website a few weeks ago, no modification. It was a Pro version if I remember correctly. I tested it on a 2015 Surface Pro. I was already connected to the network and did not click “Domain join” (I would have if it had asked for a MS account).
Just an update because I just figured what happened: I booted the iso through Ventoy, and just saw today that by default Ventoy injects register entries to bypass the online account requirement (as well as the hardware checks). Good to know.