Hi @Reprobus R,
In my test, I found that the video on the YouTube homepage cannot be added to Edge Collections. But the video content of other sections can be added. So, after studying the videos that cannot be added on the homepage, I found that when I turned off the "Video previews" option of the YouTube video, it can be added normally (as shown below). So, you can turn off this option and try adding video to collections again.
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Best regards,
Jinxin Wang