I cannot reproduce your problems using my Samsung Galaxy S9 FE.
I can reach the more button here easily. Can you reproduce this issue here at meta?
It is likely an issue with the theme at https://resource.dopus.com/. Can you reproduce the issue in safe mode, so when you open https://resource.dopus.com/?safe_mode=no_themes? Issues with themes are the reason why it is usually more helpful when admins ask for help, because they are responsible for their customizations.
And I can also scroll within the composer while the keyboard is closed