Never mind I sorted it. I will record it here in case anyone else hits this bump.
FWIW I don’t MTB… no mountains near here nor much in the way of trails. Not that I wouldn’t mind giving it a go.
Anyway the update automatically refreshed the Trailforks map. Since I don’t use it I hadn’t authorized the Trailforks maps. So I could have proceeded with the error on the road no bother. Since it was a bit of an irritant I cleared it by registering with Trailforks.
Easiest way to do it was to Open the Connect App while the Edge was connected. On the edge go to Navigation> MTB trails> login. Then follow the dialogs on the App to register. There is an authorization email you have to hit. Then you have to reboot the Edge a few times and log back in to Trailforks and authorize the map…
Alternatively you could disable Trailforks… but I couldn’t work out how.
Still no word for Garmin bless their overworked socks!