Black screen when trying to chromecast Amazon Prime and many other streams

Update
Finally found the cause, please see my post for solution and background: 

https://techcommunity.microsoft.com/t5/discussions/black-screen-issue-when-streaming-cast-finally-solved-for-amazon/m-p/3115815/highlight/true#M51933

Hi all,

I don't know if it's just me, but chromecast only shows a black screen on many embedded video streams, e.g. Amazon Prime, ran.de... either on Edge Stable (96.0.1054.62), Dev (98.0.1100.3) and Canary (99.0.1113.0). 

It works like charm on Chrome and Chrome Canary (haven't tested on Chrome Dev), so it should work on Edge as well, or?

There's not much to adjust in edge://flags anymore and deactivating hardware acceleration also doesn't solve the problem. Any suggestions or is it really a bug?

Btw, chromecast works in general on my Edge installations for the usual streams like youtube.com

Regards