Good evening, @Adyn.
Do you have an active Excel, Microsoft Office, or Microsoft 365 subscription? If not, this is likely due to an expired subscription or your permissions for Excel have changed. It will stay in Read-Only until you make the program Active or if you get the permissions changed. If the issue persists after reviewing the details of the program, please leave a Reply so we can look further into this behavior.
I'll keep a close eye out for your response. Talk to you soon!