If super mario maker 2 was on a computer, I would just take a screen video capture thing. But since its on an switch, I cant and I don't know how to film JUST my switch.
I see some people do it, so I wondered just how they did it.
Can anyone help me out here?

You press and hold the button below the d-pad.

Personally I use this: https://www.amazon.es/dp/B00005141S/ref=cm_sw_r_wa_apap_pCaQSJPQhu2oa
It's economic, it records and streams in 1080 and has close to zero input lag.

But eventually, the video cannot be viewed if you send the share link.