When trying to select text inside the content element(with "readOnly" enabled) the selected text gets deselected upon right mouse click so it's impossible for the user to copy it via the context menu.
In my POV the problem comes from the clearSelection method in SelectionHandler class which could be evolved to respect the read only mode.

I patched it locally with a simple
if(this.readOnly) { return; }
in the beginning of the method.

This suits my needs but as I'm not familiar with all the features it is possible that it's a very usecase realated fix and will break some other usecases I don't use.