EDIT: The LG UltraFine 5K works perfectly under Windows 10 at full resolution stably and with no tearing issues. This tells me the Framework firmware is fine as of now. I’m using the Apple’s 0.8m Thunderbolt Cable.
On Linux, I can confirm that it works great using Apple’s 0.8m Thunderbolt Cable. Longer cables, including the supplied cable with the monitor, did not work. This seems to be a firmware issue with a fix in the pipeline.
EDIT: I’ve found that on Wayland on Linux, there is screen tearing vertically in the middle when scrolling and moving content. In addition, night light only applies to half of the screen. There is an open issue on mutter and a in-progress merge request to fix it.
EDIT: Not so great on Linux with Wayland. Occasionally, the second display port stream stops working and it takes a mix of reconnecting and power cycling the screen to make it work again.
EDIT: Tracking the issue on drm/intel bug tracker.