apple watch 6 no longer reconizes sim
The watch is cellular and did work properly, but now it doesn't see the SIM in it and doesn't make calls.
Apple Watch Series 6, watchOS 10
Question marked as
Did you already force restart your watch by pressing and holding the Digital Crown and the Side button together for about 10sec, until the Apple logo comes back again?
Also force restart your iPhone:
Force restart iPhone - Apple Support
Also check for updates to your carrier settings and open the WatchApp/Cellular on the iPhone and see if there are any errors mentioned.
Does the button for the cellular connection turn green, if you tap on it in the Control Center, as described in this article?
Set up cellular on Apple Watch - Apple Support