Hopefully this helps +1 the OP’s complaint. Without any changes (I’m on stable branch), I also have the same error even when you click play on an existing video that used to work:
I’ve tried, via mobile, bypassing office firewall, disabling Cloudflare. No fix yet.
Testing here is mixed with error in the editor but displays in the forum:
Update:
YouTube recently tightened its policies so that new embed codes now include referrerpolicy=“strict-origin-when-cross-origin” along with updated allow attributes. I found this article:
https://blog.scriptnet.net/how-to-fix-the-youtube-error-153
Without these, YouTube rejects configuration requests from the iframe and you see Error 153.
Also see: