A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
Hi,
May I ask if your Microsoft 365 Copilot account has a work license?
Copilot works in OneNote on Mac if you have a work license. However, with an eligible Microsoft 365 Personal or Family subscription, the Copilot feature in OneNote is currently supported only on Windows devices. This explains why you can use Copilot with other Office apps except OneNote.
Reference Source: Copilot in OneNote for Mac
It may not be the outcome or solution you were hoping for, but I hope this helps address your concern.
Stay Safe!