There’s no real reason why you shouldn’t use PNG for a frame of video. I’m not talking about using it as a video format, I’m talking about extracting a frame from a video and sending it off to an editor for inclusion in another video or image.
As a user, I would expect that I could use the most popular lossless image format if I want to losslessly share a frame from a movie with someone.
Of course I do agree that we need adoption of other image formats. We really should not still be cramming everything in PNGs or JPGs in 2023.