This is it ^^
I’m on Ps5 and like SlouchyBard, I just send the screenshot to myself via the PlayStation mail and go to the PlayStation app (you find it on Apple Store), get the picture back via the app messagerie and save it to my iPhone gallery.
Then I post it on imgur (always on “hidden”), imgur has an app too. And I finally grab the link for sharing on the forum : a BbCode one between 2 [img][/img] tags.