You need to use the embed. Right click on the video and get the embed code. Links are not allowed in top line threads (to prevent spammers.
Here is a post I did about it explaining it. Can embed a lot more than YT.
https://inleo.io/@taskmaster4450le/premium-members-how-to-post-videos-in-top-line-threads
Thank you, I'll do the right way this time.