Given their other post, a Nintendo Switch, so an HDMI capture card. Those can be pricey.
Yeah, I have the Nintendo Switch and Macbook Air which isn't the best setup, but it's all I can afford.
MacOS makes your setup a bit more complicated, it can be tricky to find a capture card that actually has drivers for Mac. Often times, the big name brands that offer cards with those types of drivers, like Magewell, Elgato, some StarTech models, will run around a couple hundred dollars. You might be able to find some plug and play solutions, but I can't vouch for their quality. I guess it really comes down to what your budget is for a capture card. Otherwise your other option is point a camera (phone, webcam) at the TV and record that way. The quality is obviously bad, but it's the cheapest option by far.