Nick,
I also run a Pi4 here.
The behaviour you described seems to be all right. The red light went off after boot and the green light starts blinking. After that you have to wait for quite a while and then the rooExtend WiFi should show up. Please give it five to six minutes and check again.
I wonder if it has something to do with the country code. I put the settings of rooExtend in the technical thread. Please let us discuss this topic there…
rooDial technical integration discusions - Audio Products - Roon Labs Community