Possibly either related to the bug mentioned here or its fix.
As before I’m using latest iOS 12 and Safari, and it’s reproducible here on meta. When typing a reply, clicking “Done” on the keyboard previously unpinned the reply box so that you could scroll through the topic. Now the keyboard just hides with no change to the Discourse UI, so the reply box still covers the whole page.
I think there are two more issues on iOS 12. Feel free to split the topic if I should have made new topics again.
Selecting a user from the list shown after typing @ has the same effect that selecting an emoji did. This one isn’t reproducible every time though. But it seems to happen often enough that it’s an issue.
If I’m in the middle of composing a reply and I leave Safari (switching apps, screen locks), when I open Safari again the reply box is no longer covering the whole page, and the page itself has scrolled up. This one happens every time. I do this often enough that I’m also pretty sure this bug is relatively new.
EDIT:
Did the reply box used to exit full screen when selecting menu options like hide details and blur spoilers? I can’t remember on those, but selecting either of those is now doing that. Sometimes even just selecting the gear icon is causing this, but that’s not happening every time.