what it sounds like, is you just can’t set, watch, or record from channels, and you already had a antenna setup in dvr.
If this is true, it is likely because plex only allows 1 epg (program guide) at a time currently…, a lot of us are hurting because of this.
If this may be your problem, and you want full guides for both ota and cable, then please vote for Multiple epg sources, for those with multiple tuners , which I had started, after facing a choice of either loosing cable channels, or ota.
For the short term, you can either, make your own epg, with all the sources you need, then set up the individual channels by tuner…, or, you can chose one source, and waste hours trying to match the cable and ota channels, and likely not have all available channels… I did the later, some have tried to do the former…
If plex ever got the drm management to handle drm, it would likely be a plex pass subscriber option…