I'm not sure you're able to embed YouTube videos like that – IIRC they serve them up in a format iOS doesn't support without special permissions from Apple. Perhaps try a direct MP4 link first and see if that's better.
Yes I tried with local m4v files, its showing black screen. Tried mp4 file it shows the video thumbnail but no controls, does not play. A remote url works but not youtube video. I need to play local m4v files. Also how to programmatically play the video in swiftUI and also add flag overlays as this is a test.