The error suggests a 404 page may be getting served, try going to that url, what do you see?
Perhaps you need to rebuild NodeBB?
i can find the attach picture icon for a post in PC, which is the last in the list of icons.
With my iphone x max, i cannot see it unless i turn 90 degrees, this is not good for the new users.
@ningji You can scroll the menu with editor items at the top.