Just chiming in that I’m also seeing this error on my game: https://opyate.itch.io/pop1
These headers work for me locally:
“Cross-Origin-Opener-Policy”: “same-origin”
“Cross-Origin-Embedder-Policy”: “require-corp”
Newgrounds supports these headers: https://www.newgrounds.com/bbs/topic/1468978
Thanks for spending time on this!