Dear respected,
According to the description, we understand that you are seeing all your OneDrive files in Read-Only mode. If so, it is possible that your school admin has retrieved the related OneDrive license from your school account.
To confirm this, please check if you can sign in to OneDrive Online via browser and still all files are read-only there? If you will be able to create a new file there? If not, we suggest that you confirm with your school admin or IT department that if your OneDrive license has been reclaimed by the school. Besides, we suggest you check with other students at your school to see if they are seeing the same issue.
Meanwhile, you can also confirm your license status in My Account (office.com), click on the Subscriptions tab, and search for a license called "SharePoint plan" which is the one that allows you to use OneDrive.
Feel free to post back with me if you need any further support. I appreciate your time and effort in checking these above and thank you for your time and cooperation. I hope you're staying safe and well!
Sincerely
Mia | Microsoft Community Moderator