How to highlight a screen session of an ssh connection?

Others have asked ([How to scroll inside a screen session of an ssh connection?](https://unix.stackexchange.com/a/454399/400310)) on how to scroll within a screen session. However, while I can highlight what is shown in front of me, I can't figure out how to highlight and scroll (i.e., to copy more of the output). Highlighting with my mouse does not let me scroll via page up/down or other means I've tried.