This occurs here and in our community as well. I have tested with iPhone 16 iOS18.3.2, Safari and Chrome.
This occurs when starting new topic, or when replying to the existing one. I have took screenshots to show this behaviour.
Lets start with the situation when starting new topic. If you havent done anything, view is ok:

But when you tap Title field, look what happens. Right side of the view is hidden.

And when you tap the text editor, look what happens. Left side of the view is hidden.

Here are the screenshots when replying to the existing topic. If you havent done anything, view is ok:

But when you tap Title field, look what happens. Left side of the view is hidden.

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Mostly this is cosmetic issue, it feels and looks weird.
I am not sure are these related together or not, but another observation:
It seems that, depending the device you use, it is possible that Category drop down menu cant be fully seen (right side is hidden) and it confuses users. This is screenshot from Honor 200 Lite:
