I've tried installing the extension by running sudo apt install gnome-shell-extension-multi-monitors, reloading the shell, then enabling it via gnome-tweaks. However the enable button is greyed out and it says "Error loading extension". I also tried installing it following the instructions on git https://github.com/spin83/multi-monitors-add-on but the results are the same.
The error seems to be "JS ERROR: Extension multi-monitors-add-on@spin83: TypeError: this._onButtonPress is undefined".
I am running Ubuntu 20.04.2 LTS with gnome version 3.36.7