UHD Blu Rays cannot read on Xbox Series X actually

I ended up doing that as I was a bit worried about the optical drive in my Xbox One x when it refused to play certain 4k Blue ray disks.

My old Xbox One X had issues with some UHD movies, so much so that I too bought a stand alone UHD Blue-ray player. Playback issues were (probably still are) common on the One X. I've never played a single Blu-ray, UHD Blu-ray or DVD in my Series X.

There really isn't any need to test all of the discs. Test a few. If the discs are in good clean order they would have played on another BD player.

To be fair, on the Xbox Series X official page, there is no mention of 3D so it can't be expected:

"Optical Drive. 4K UHD Blu-Ray"

As to not having a state of the art player, not surprised there either....a £450 ($500) console is not expected to have a blu-ray player that would cost probably £200 standalone

Xbox One discs are Dual Layer BD-ROM discs 50 GB, which is pretty much standard now. In addition, the One S and the One X can also read UHD Blu-ray feature film discs. Neither the One S or One X can read BDXL discs, I don't know enough about the hardware
to say for sure if this is due to a hardware or software issue. Note that despite the similar storage capabilities, UHD Movie Blu-ray discs are factory pressed, while BDXL is a writable format largely for burning discs with a PC.

Despite the One S and the One X's ability to read UHD discs, they will not be used for Game media.

Its a dvd

Nope, not quite right.

Original Xbox - DVD

Xbox 360 - DVD (or more specifically, DVD-9).

Xbox One - Blu-ray

Xbox One S and X - UHD Blu-ray drive, but games still on standard Blu-ray.

Scarlet will have a UHD BD drive so that can still play all formats of movie discs. Likely that games will be on 100GB discs.

Im playing from the 4k uhd player in the xbox one x

The blu ray player is up to date yeah