Hi, I use Office 365. I save my files to my computer (not to the cloud).

Previously, when clicking X on a Word doc to close it, it would prompt you to save it and you could rename the file.

Today, I see a different screen :

Save your changes to this file?

The Filename field is greyed out. I cannot change the filename.
The Choose a Location works. I can change the location.

The buttons underneath are : Save | Don't save | Cancel

Has this happened to anyone else? Is there a way to revert back?

I guess I never close out of a file that way. Old-school habit, I hit File, Save As.

It may be dependent on what your default file location is. File/Options, select Save on the left bar, and check the default local file location found about 3 inches from the top. If it's going to your "Documents" folder, that may be preset in 365 to back up to the cloud (OneDrive). Mine is, and my Desktop is, but we save most of our documents to project folders on a shared drive.

I do not edit important documents in the online version.
If I did, I would, upon opening the document, use Save As to save to a different name.

If you prefer to save locally on your PC, ensure that you select "Save to Computer by default" at File > Options > Save. You may also have to specify a "Default local file location."

To save any document under a new name, you can use F12 (or Fn+F12 on some keyboards) to go directly to the classic Save As dialog box.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional