When using an external monitor/projector with Emacs, I use the Extend option (rather than Duplicate). Then I duplicate my work frame with
C-x 5 2, that is
make-frame-command, and I move the duplicate frame to the projector screen.
I further use activate
(setq cursor-in-non-selected-windows 'bar)
With this setting what I write on my laptop frame is mirrored on the projector frame, provided the it is set to the same buffer.
My problem is that I can't mirror the selection highlight, which unfortunately is shown only in the frame where I am actually writing/selecting.
Any possibility to do this?