I don’t usually torrent, but I just looked at recent eps from Usenet and it looks like the majority is 1080p max. 4k exist, but tend to be from streaming services like Netflix, Hulu, HBO, or AppleTV it seems.
I find NZBFinder to be a decent usenet indexer for free, so maybe take a look on there for the shows you’re wanting and see if they’re even out there. It could be they just aren’t available at all.