Hi Boian Soloviov,
I am not an expert in Microsoft 365 subscriptions, but I focus on providing technical support. The solutions I provide are all from Microsoft support articles that are publicly available on the Internet.
If you cannot downgrade your subscription to a version without copilot according to the instructions in the article, please contact online support: steps mentioned in the first reply of this post Remove Copilot - Microsoft Community
Feel free to contact me if you have any questions, I am here to help you further if needed.
Best Wishes,
Stan.L - MSFT | Microsoft Community Support Specialist
I, too, have spent DOZENS OF HOURS attempting to remove Copilot and searching online and trying all sorts of settings, in addition to being unable to open week after week of emails from childrens' teachers when they include attachments because of it. I, TOO, PAY FOR THE EXPENSIVE UPGRADE AND CAN FIND NO WAY TO DOWNGRADE IT WITHOUT LOSING. ENOUGH! What is the answer? WE do not want AI in our email, NOR DOES IT EVEN WORK! Please. Thank you.