You know where you find it? Under Settings -> Storage -> Console Storage -> Media Gallery -> USB. I don't know if it's changed or what since this YouTube video was posted, but I can't get Media Gallery to show up on the home screen under either Games or Media. But in fact, as much as I looked, for me it doesn't show up there. But the thing is, the guy talks about (and shows) a 'Media Gallery' app that you're supposed to be able to find under the 'Games' tab (rather than the 'Media' tab. I Googled it, and found this video explaining how to do it.

I suddenly wondered if the PS5 could even play video.

On PS4, when I plugged in a USB, the Media Player app would pop up. Since it's premium content, it's not on YouTube, so I downloaded it, loaded it onto a USB, and plugged it in to my PS5. I haven't really had the need to play any video files on my PS5 before now, but I saw the Hitman 3 Playdate posted today and figured I'd put it up on my TV as background stuff to watch while I got some work done on my PC.

Ps5 universal media server