Uploaded a 5K video to YouTube, but it doesn't show 5K in the view option (only 4K and below)

Question

I've uploaded a 5K video to YouTube, but it doesn't show 5K in the view option (only 4K and below). What could be the issue?

5K video codec, FPS and resolution as shown by VLC (recorded by a GoPro 10):

YouTube displayed "Processing HD" at first:

Once done, the YouTube player only offers 4K and below:

I tried re-encoding the video through handbrake to downscale it to 5120x2880 and send it to YT at that resolution but that didn't work: still only 4k, no 5k on YouTube:

However, YouTube does support 5K, e.g. https://youtu.be/0aOREFhSafE is 5K:

Answer 1

According to a few Reddit posts, the issue is on YouTube's side. E.g., from Reddit user footofwrath:

I make VR videos using Insta360 cameras with native resolution 5760x2880s - 5K. For two years every video shows up with 2880s 5K option. But between 27 Jun (last good) and 2 July (first bad) 5K option seems removed.

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Update 2022-09-20: https://support.google.com/youtube/answer/6375112 finally updated their documentation, 3 months after the issue started:

Note: In 2022, we started removing support for playback at resolutions between 4K and 8K. For example, we may no longer support playback at 5K.

Thanks to Reddit user HillMoore for pointing me to it.