I just double checked on my MacBook. Getting into fullscreen works fine with the button on the video, getting out works fine with the button and with the esc key. Sorry not helpful, but it may not be a universal Mac problem?
... ; Shut Down.
After your Mac shuts down, press Shift-Control ... again to turn on your Mac.
If the battery is ... removable:
Shut down your Mac.
Remove the battery. If ... again to turn on your Mac.
Oh yeah, you just mean like a monitor? It’s pretty simple. You might have to get an adapter cable of some sort, depending on the monitor and your laptop. This is how we have our set up at my office, we all have Mac laptops with external monitors.
I know the post is labelled as "solved," but if anybody else attempts to transfer videos from an iPhone to a Mac, Image Capture (per-installed on Mac) is a great application.