Steps to reproduce
Click on the share button on any website in safari or any other app, choose Supernotes in the Share Screen, then Supernotes opens but no card is generated.
I have a similar issue on Android. Maybe it is even the same? For me, sharing works if the app is not running at the time of being selected as the target to share to. It fails if the app is running in the background. Is it the same for you?