Obviously I have several things to debug here as I literally just set up the server (searching Reddit to see about the audio). I literally tried it then jumped to Reddit, found this thread, so this is in last 15 min. Sorry for the long post this is quick stream of consciousness post - Wanted to update this as I'm in KC also and just set up a new Plex server on my QNAP in a Windows VM (long story why Windows.) But I DID (accidentally) see the ATSC 3.0 channels in the guide in the 100+ channel range, they did automatically show up on Plex OTA TV Setup, they just weren't autoselected, I checked internet to see if that's 3.0 and yes it exactly matches the stations doing that as of 8/2021 - So I selected them and associated them with the 1.0 version's guide - technically it's working (still minus audio) - tho very sluggish and halting. I've yet to see anything actually broadcasted in 4K though. Side note though, the ATSC3.0 channels do work in the Channels iOS/tvOS apps, as well as the HDHR native apps (with Audio). I tried adding the ATSC3.0 channels with the ATSC1.0 Channel Guide data, but the ATSC3.0 channels don't even show up in Plex, regardless of guide info being available. Whatever TV Guide provider Plex is using hasn't been updated to reflect the new channels. The new channels actually do show up during setup, but the channel matching with Guide data doesn't show any of the new channels (100-200), and you can't re-use an existing channel (in KC market they are still broadcasting both ATSC1.0 on 0-100 and ATSC3.0 on 100-200). They recently rolled out ATSC 3.0 in KC last week, and I was eager to test in Plex. It does receive all the ATSC 1.0 channels perfectly. I have the HDHR5-4K (Connect 4K), which is the early adopter/beta of the Flex 4K.

Plex hdhomerun 4k