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Let me break it down for you. The same process used previously now doesn't work. The videos in prior posts added in exactly the same way are still playing. I can't even insert the video used previously or a new video anymore in a new post. There is nothing different about the process or the post. If I copy the code from a prior post and add it to an embed snippet, or the post's source, it is stripped out when saved.
What is the point of having an "insert video" tool if it doesn't work?
Nothing has changed here so perhaps you could look into recent updates over I'd say the last month and let me know what you've changed. Based on the number of bugs reported, it's obvious Msft doesn't test updates properly so that's most likely the issue.