I have a Lightroom Classic CC Ver. 8.2.1 shared "Collection" with still images and a few .mp4 video files on my Mac Mojave desktop computer. The video files are visible and playable fine on Lightroom on the desktop. However, the video files don't seem to synch to the corresponding synched Lightroom shared Collection on other devices, or on the Lightroom online web site. I don't get any errors. Simply, the video files appear not to "synch" outside of the Mac computer. All other image files synch fine. If video files are not supported, this shortcoming should be very clearly documented, and it isn ́t. Plus, the user should get some sort of error message, which is not happening right now. I hope this feature gets implemented very soon.