The LG UltraFine 5K Display is not available for purchase in the United States, the UK, Canada, and Brazil, as noted by 9to5Mac. Prior to when the monitor was listed as unavailable, there were long shipping times after purchase, which suggests there could be possible supply issues.
If supply issues are indeed at fault (and supply problems have also caused long shipping times for other Apple products like the iMac), the display’s unavailability is likely to be temporary. Apple has not provided details on whether the monitor is temporarily sold out or no longer being sold, however.
Last May, the 5K LG UltraFine Display was also listed as unavailable from the Apple Store prior to a refresh in late July 2019, which is the model that was purchasable up until recently. Apple is continuing to offer the Pro Display XDR, but that is a much more expensive display option at $5,000. The 4K LG UltraFine model is also available for purchase.
The Thunderbolt 3 LG UltraFine 5K Display offers a 5120 x 2880 resolution with 14.7 million pixels and P3 wide color gamut, plus built-in stereo speakers, a camera, a microphone, and an adjustable stand at a $1,300 price point.