And in case somehow facebook decides to have one of those videos… it is 99.9% possible they prefer 1080 than 4k. Facebook is not a video website. Its reason of existence isn’t the streaming of videos. They may have some for entertaining purposes, but they can’t afford having 1080 or 4k capacities.
https://www.quora.com/When-will-we-see-1080p-or-4k-on-Facebook