Hello,Leah Miller1
Welcome to the Microsoft community!
I have realized that you want to turn off Copilot.
Before that, I would like to ask you for some information to better address your question.
What is your current Office subscription? Are you currently a Microsoft 365 Personal Edition subscriber?
According to your reply, you should not have a subscription to the Copilot Pro version.
However, we recently received news that Copilot will be added to Microsoft 365 in some regions.
This should be the reason why you are having this issue after updating.
Unlock your potential with Copilot and Designer in Microsoft 365 Personal and Family - Microsoft Stories Asia

Since this is an officially pushed update, the only way to confirm if there is an option to turn off the feature is through feedback at this point. Or rollback to an older version.
How to revert to an earlier version of Office - Microsoft Support
You can confirm your current version of Word by clicking File > Account > About Word
Search for "CMD" in the search box in the bottom left corner and run the command prompt as administrator.
cd %programfiles% \Common Files\microsoft shared\ClickToRun
Press Enter when you are done typing and type on the next line
For example: April 9, 2024, version 2403 (Build 17425.20176)
Officec2rclient.exe /update user updatetoversion=16.0.17425.20176
(The version here is the April version, you can follow the link below to choose a similar version time)
If you're Microsoft 365, you can check this connection
Update history for Microsoft 365 Apps (listed by date) - Office release notes | Microsoft Learn
How do I give feedback on Microsoft 365? - Microsoft Support
Feel free to post back if you need further assistance.
Thank you for your understanding and patience and I look forward to hearing from you.
Ryan - MSFT | Microsoft Community Support Specialist