[makeworld]

You can totally do that! See the section on Format Selection[0].

From my reading of it, doing this would work for what you want:

  -f 'bv*[height<=720]+ba/b[height<=720]'

[0] https://github.com/yt-dlp/yt-dlp#format-selection

[emptybottle]

Alias that to

  -f 720ish

and we’re getting somewhere

[1una]

Maybe you are looking for

  -S res:720

https://github.com/yt-dlp/yt-dlp#sorting-formats

[IronWolve]

Also want to save it in .mp4 format, trying it saves it formats in .webm

[1una]

Well, that's

  --remux-video mp4

https://github.com/yt-dlp/yt-dlp#post-processing-options