@JPEG When writing a toot reply, the up and down arrow keys on the keyboard do not move the text cursor up and down one line as they do normally on macOS. Instead, they cause the window contents to scroll. When you hit the down arrow, the top of your toot is hidden. When you hit the up arrow, the toot you are replying to is revealed (and there seems to be no other way to reveal this!).
This Mastodon instance is for people interested in technology. Discussions aren't limited to technology, because tech folks shouldn't be limited to technology either!