Hello ArcGIS Online Team,
We have encountered an issue with new JSAPI 4.x applications, they do not support videos embedded (iframed) in popups. All applications not not on the JSAPI 4.x framework do support these videos. We have opened a support case and it appears to be a known bug- BUG-000129037 logged 6 months ago. Here is a list of affected applications- https://community.esri.com/docs/DOC-14455
This issue directly affects us from using any of these new tools- any updates would be much appreciated.