I’ve had the idea of recreating tv channels on my plex server by using tv guide data from the late 90s early 00s

The insurmountable part of that project would be getting the guide data.

You don’t know what other people will want in the future

That's a great idea.

There's are sites that stream old content with a old tube tv UI wrapped around the video frame but they don't have all the commercials and they don't follow the old schedules like you suggest.

I've got a friend who has hoarded digitized copies of VHS recordings of old cartoons from that era complete with the commercials, so the content is definitely out there.