I totally understand the inconvenience this issue has brought to you.
There are other users on the Internet who have reported the same request.
If needed, you may try to create a second window (View>New Window), then minimize or close the first one. Based on my tests, this icon does not appear in the newly created window.
(This workaround is shared by Williams, Carrie from thread: How do I remove the Copilot icon from slide view in PowerPoint?)
Besides, I suggest you vote up this thread: Copilot icon in slide view is a major annoyance. More people vote for it, the need louder.
Thanks for your understanding.
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