The extensions that can be uploaded onto Media Sharing are
mp4’s video codec H.264 and WebM’s vp8 and vp9.
Please check if the extension of the file you wish to upload is any of these.
Check if an emoji is included in the name of the file you wish to upload onto Media Sharing.
If an emoji is included in the file name, the file cannot be uploaded.
Also, a video whose size is greater than 2 GB cannot be uploaded as well.
In such a case, please share a video via Screen Sharing, instead of Media Sharing.