Yes, it really is confusing. DV has so many different variants it’s hard to keep them all straight. There is single-layer with no fallback, dual-layer (with fallback, obviously), and single-layer with fallback.
The specs from the IT sample show this is profile 8, which technically has one video track, but includes an HDR10 fallback.
HDR format : Dolby Vision, Version 1.0, dvhe.08.03, BL+RPU, Blu-ray compatible / SMPTE ST 2086, HDR10 compatible
What I imagine Plex is doing is playing the underlying HDR10 video, but switching your TV to DV. This is technically incorrect, as the video being played is the HDR10 video, without the extra DV info. You could get the same effect in Infuse by enabling DV in the Apple TV settings, and then disable match dynamic range.
What MakeMKV can do is recreate dual-layer DV files, and keep the separate HDR10/DV info. For example, it cannot combine dual-layer videos (IE UHD Blu-rays) into single-layer (without fallback) DV profile 5 video.
There are other apps which capture the HDR10 video, but add metadata for DV Profile 5. This is also incorrect, as the underlying video is just HDR10 and not DV.
Analyzing the underlying video takes a bit of work, but a super-quick way to check if something is actually single-layer (with no fallback) would be to play a sample in IINA on Mac (which does not support DV).
Here’s a comparison with the samples found at: https://developer.dolby.com/tools-media/sample-media/video-streams/dolby-vision-streams/
Profile 5 (no fallback)
Profile 8 (with fallback)
As you can see, IINA is unable display the correct colors in the DV-only file. But is able to display the correct HDR10 colors in the file with fallback.