A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
Hello Mia,
Let's try to figure this out before throwing fixes at it.
Since you already checked on multiple devices and browsers including incognito, we know it is an issue with the account or the cloud server itself and not just a weird app glitch.
Just to be completely sure about the situation, what is the exact error code or message you see when you try to open one of these excel files on the web? Also, if you create a brand new file in that same OneDrive folder right now, does it let you save and open it properly or does that get restricted right away too?