I'm not sure what the difference between our experiences but I tried this same thing for videos on MS Stream, Vimeo, and YouTube. Used the same exact prompt and several variations to try to produce the right type of response.
It says is looking for a video to summarize, then... "I’m sorry, but I need more information to summarize the video. Can you please provide more details about the video you are referring to?"
I also tweak a few settings and I get it to say. "Certainly!.... If you’re looking to summarize a long YouTube video, there are several AI-powered tools that can help you achieve that. Here are a few options: summarize.tech, VidSummary, QuickRecp.ai, Video Summarizer by Mindgrasp AI, YouTube Summarized and several other products."
I have an enterprise Copilot license, I'm logged into my work MS account in the Browser, I'm toggled to the "Work" versus "Web." Other coworkers do get it to work.