Thanks to one and all.
I've been a Kodi user since 2014 sometime. My WDTV player died, and a friend gave me a Kodi-based Pivos player as a birthday to replace it. One Pivos, two non-name Android players, and a linux-based Arnu box (which was great, until it died and the company was dead with it) later, I bought an XBox One S in 2019 solely for the fact that it's the reference Kodi platform. I've yet to play a game on the thing, using it only for Kodi, Amazong Prime, Youtube, Crave and Tubi, and I've never regretted it.
That is, with the sole exception of upgrades. Every single time Kodi's upgraded on me
something gets buggered. I've lost audio, Samba support, subtitle downloads, and this time video playback. I don't install or run add-ons (except for subtitle downloads), because Kodi's been rock solid, and if it works, don't fix it. Like @
docsonhammer above, I've regretted it every time it's upgraded, so I simply don't bother.
Unfortunately, I had a power failure today, and on rebooting, my XBox took it upon itself on power up to upgrade every app, so my Kodi 19.3 became a video-less Kodi 20.1.
Fortunately, experience has taught me the first thing to do is to check out forum.kodi.tv and see who else has the same problem, and sure enough, this thread had the solution. Switching from "Auto Detect" to "DXVA" has worked, at least on the three videos I've checked so far.
So, thanks again to Team Kodi and all the helpful members of the forum.