I have the same issue. I open an excel file with win 11 from our main computer which is win 10. Then when i hit save it says that the file is read only.
So i go to the folder that the files are inside of and right click and it has the read only box checked. I uncheck the read only box and hit apply. It then says an error occurred while applying the attributes to folder.
For some reason i can't upload screenshots of the messages. It keeps saying failed.
Here is a link to the screenshot which is in my drop box account.
https://www.dropbox.com/scl/fi/vvlq68jc8ezh3x3ksyosc/error.jpg?rlkey=z3roomb3jqqkjxhb71qa203tw&dl=0
Thanks in advance for any help you may provide.
To add screenshots here, just paste. No need to use any upload feature. Anyhow, it sounds that you have an issue that is causing your Excel file(s) to become read-only as opposed to the folder.
You stated "So i go to the folder that the files are inside of and right click and it has the read only box checked".
It must have looked like this:

As I've stated multiple times here, that "checkbox" is just a control to allow you to set or unset the read-only attribute of the files within the folder. It does NOT indicate the read-only status of the folder itself and it does not even tell you if one or more files within the folder are read-only. It will look like the above picture even when zero files in the folder are read-only. It's not a status indicator. It's just a check box that has been misused as two-way control. Microsoft should be forced to change this interface because it keeps confusing people.
When you clear that box and click OK, Windows tries to set ALL files within that folder to not be read-only. It will error out on any files that are locked (i.e. open in Excel or otherwise being used).
Open the folder and look at the individual file properties. Do they indicate read-only? If so, can you change the read-only property for the problem file (after ensuring that the file is not in use - you may even have to logout and login)?
When Excel reported that the file is "read-only" it may not have been due to its file attributes. It may be due to its state. I'm not sure how Excel handles sharing, but with some programs, its possible for two users to access a file with one user having full change rights and the other user in a read-only state. These are issues that typically only occur when a network is involved (which I understand is the case here).
If you want to confirm the read-only status of a folder, open a Cmd prompt and enter the command attrib foldername. For example, attrib c:\test will show R if the folder c:\test is read-only. But it's a moot point because a folder being set to read-only does NOT prevent files from being created, changed, or deleted within the folder. It only prevents the folder itself from being easily deleted.
Permissions are a completely different thing and people often confuse the file or folder read-only attribute with read-only permissions in NTFS or a network share. Maybe you have a permission issue, but it sounds like a bug if the file was fully writeable and then suddenly you're locked out. Maybe a network share related bug. I suggest starting a separate discussion or find discussions that deal with Office file lock out issues on a network share.