Final result:
How to embed YouTube videos

Just get the link of the YT vid and paste it in the Source box when you click Insert Media, That is way easier

I believe you have to use the embed code, say:
<iframe width="560" height="315" src="https://www.youtube-nocookie.com/embed/yhqV49us4J8" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
Not the the link, say,
https://www.youtube.com/watch?v=yhqV49us4J8
Fastest way:
1) Right click video
2) Click "Copy embed code"
3) In the chess.com editor, click the "media" icon
4) Click "embed" and paste the code from youTube
Alternative way:
1) On youTube click "Share"
2) Then still on youTube, click "Embed"
3) Copy the code
4) In the chess.com editor, click the "media" icon
5) Click "embed" and paste the code from youTube