tl;dr
Running LibreELEC 12.2.1 (Kodi 21.3), a Beelink S12 Pro N100 box starts all HDR10 material in SDR, switches to HDR a couple minutes later, then switches back to SDR after a few seconds. Kodi debug log:
Background
I recently had a Sony A80J OLED replaced with a Sony Bravia 8 under warranty. I had been using a Beelink S12 Pro N100 box running Windows 11 Pro with the A80J, and it was a perfect Kodi device, matching refresh rate and resolution, doing HDR10 and everything else right. I hooked it up to the new XR80, and it just fell apart. The resolution switching took a lot longer, and playback initiation was accompanied by the UI flashbang I've observed with Android devices like CCwGTV and Onn boxes, where the screen goes black for a second or two, the Kodi home screen flashes, and then playback begins. Also, HDR was broken. HDR10 movies would start out in SDR, after a couple of minutes switch to HDR, then switch back to SDR a few seconds later.
Troubleshooting (done for both Windows and LibreELEC)
My TV inputs are correctly set to Enhanced mode. I was using Monoprice Ultra High Speed HDMI cables, but I tried one from a different brand and got the same results. I tried a different TV input, but no joy. I tried my CCwGTV on the same inputs where the N100 was failing, and it worked perfectly with HDR. I tried my main PC running Windows 11 Pro with an Nvidia RTX 3060 Ti, and it worked fine. Since Kodi ran perfectly as a native app on the TV, I concluded there was an incompatibility between the N100 and XR80, gave up, and planned to sell the N100.
LibreELEC
I've found it useful to have a backup Kodi device so decided to keep the N100 and try LibreELEC. It's definitely snappier than Windows 11 was loading Movies Wall view, so that's nice. It also doesn't suffer the slower resolution/refresh rate switching with the XR80. It's as good or better than the N100 running Windows was with the A80J, except the HDR issue persists on the XR80. I've linked to a debug log where I play an HDR movie. It begins in SDR, and after 2:12 seconds of viewing, it switches to HDR. After another 38 seconds, it switches back to SDR. This is obvious visually, and it's also reflected in the Sony's "Detailed signal info" overlay as I'm viewing. This happened around 10:55, but there's nothing in the logs between 10:53 and 10:56, unfortunately. I first observed this when LibreELEC was using 12 bits, but I found the script linked here that limits it to 10 bits, and it didn't help.
Kodi Debug Log
MediaInfo video section for file I played
Video
ID : 1
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main 10@L5@High
HDR format : SMPTE ST 2086, HDR10 compatible
Codec ID : V_MPEGH/ISO/HEVC
Duration : 2 h 29 min
Bit rate : 16.2 Mb/s
Width : 3 840 pixels
Height : 2 160 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 10 bits
Bits/(Pixel*Frame) : 0.081
Stream size : 16.9 GiB (78%)
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : PQ
Matrix coefficients : BT.2020 non-constant
Mastering display color primaries : Display P3
Mastering display luminance : min: 0.0050 cd/m2, max: 4000 cd/m2