But this doesn’t mean we can share to Discourse yet? Guess this would require the implementation of the Web Share Target API? In any case I couldn’t find a control to do this within Safari despite having added Meta to Home Screen. So I guess that’s 12.3 … This would be the tipping point for adoption for me.
Also to report: can’t type in Composer with GBoard, a third party keyboard. Native keyboard works fine but you have to completely disable GBoard as you can’t even switch keyboards! 
Perhaps this is enforced as part of security implementation?