How to best capture footage of old gameboy hardware features

I am looking for a very easy to use but preferably non-computer way to record footage from a gameboy. 

I am specifically looking to capture footage of some rare link cable and timer functionalities of some old gameboy games.(No it’s not pokemon.)
I cannot find any footage of these specific games, doing specific functions. Mostly because all the LP’s emulate the old title and you cannot the hardware features via emulation. Additionally, I am a Mac-user.

I would prefer non-computer way, so that I can focus on just playing the game and enjoy it on the go. (I am trying to embrace what the hardware could do - while also getting some footage)

Ideally, I would love to just click a button on a mod’d gameboy and record it all to a SD card or something.

Or maybe someone has a good gameboy alt?

Additionally, i would be looking for two. So that I can record the footage on both devices as they traded.