Thanks for the heads-up, the bit at the end was a mistake.
I opened your final godot file and saw that in Project Settings / Displays / Window / Size.
Width = 1920
Height = 1080
I watched your 2 hour youtube video as well. I think the part when you switch this setting from default is missing. I saw another question from someone else on this course about it. Changing this is what changes the player size or perception of size change.
One more thing on viewport / window size. Right now I'm working on a retina macbook pro.
in Project / Project Settings / Display / Window
Under Dpi there is a "Allow Hidpi" check box. Turning this on makes my game size look most like yours. Before I was messing with camera zoom etc. If other people have goofy displays like the mac retina that maybe changing how they see things on their screen.
On my to-do list is explore more about this setting and how it might affect level design for different monitors and displays. example if you design on a retina mac and play on a linux machine how does it look and vice versa. Any knowledge you have on this setting and multi "platform design" would be helpful.
I've updated the video a few hours ago to add the missing window settings tutorial.
Regarding HiDpi, my understanding is that it would increase the resolution of the game, e.g. render on 4k instead of full HD on retina displays, possibly costing a lot of performances. Windows, Mac, and Linux desktops all provide UI scaling options on the OS's side instead.
I don't have a 4k/hidpi display to test this setting right now actually.