What phone and iOS version? The screen looks quite small vertically and I’m using a iPhone 17 here and all ok on creating new topic.
Does it help to hit the tick on keyboard bar (top) and reopen the editor?
Is it same on Edge or Firefox on same phone (despite it using same WebKit underneath)?
Does it also happen here? https://meta.discourse.org/
Does anything better happen if you do a ‘Request Desktop Site’ from the iOS … mystery tour button menus?