FEC chiming in
https://twitter.com/ChuckCallesto/status/1324785959871959040
>>11503575 /pb
If you're trying to post a Youtube URL, then go to the video in Youtube, use the share button to copy the link, then open the "Show post options & limits" then past the URL in there.
For Twitter videos (which BTW I think we've seen this one), use a downloader tool first to download it as mp4, then you can post here by dragging like image or PDF files.
https://www.savetweetvid.com/
https://twittervideodownloader.com/
https://twdownloader.net/