If a worksheet or presentation is locked for editing and can’t be edited in the Windows desktop application, it may be that the file is already being edited by someone else, or they have the file checked out.
Not sure what "checked out" means? This article might help: Check out or check in files in a document library.
Let's take a quick look at some of the reasons why you might not be able to edit the file.
The file is locked due to a previous crash
If your computer stopped working previously while the file was open, it's possible that the app mistakenly thinks the file is still in use, and thus the app has temporarily locked the file.
If the app tells you that you can't edit a file because you already have it open, try the following steps:
Close the app.
Restart your computer.
This action should release the lock and allow you to open the file for editing again.
Another author has checked out the file
Normally, for a file stored on a SharePoint site, more than one person can work on it at the same time. This is called coauthoring. But if someone checks out the file from SharePoint, other authors are temporarily prevented from working in it until the file is checked in.
If required check-out is turned on for the document library in which the file is stored, the coauthoring features aren’t available.
For more info, see Check out or check in files in a document library.
To see who has a file checked out from SharePoint:
Navigate in your web browser to the SharePoint document library.
In the list of files, find the file you want to work on. If the following icon appears near the file name, someone else has the file checked out:
Point at the file. A small pop-up window with info about the file appears. Included in the info will be the name of the person who has the file checked out. You can then contact that person to inquire when you may get access to the file.
Another author is using a different version of the Office application
If an author opens the file in a previous version of the Office application, the coauthoring functionality isn’t available. For example, if the file has been opened in Excel 2010, then coauthoring isn't available. Ask them to save and close the file as soon as they're finished in order to unlock the file for you.
This also applies to you, of course; make sure you're using the current version of the Office application.
The server doesn’t support the coauthoring functionality
The coauthoring functionality is available when a document is saved on a SharePoint Foundation site that supports Workspaces, on SharePoint in Microsoft 365, or on OneDrive. If the file is saved on some other kind of server, however, it's possible that the server it's stored on doesn't support coauthoring.
It’s also possible that your organization’s policy administrator has disabled the coauthoring functionality on either the server or on your computer.
If any of those are the case, and somebody else has the file open, you won't be able to edit until they close it.
The file format isn’t compatible with the coauthoring functionality
The coauthoring functionality can be used with Open XML files (such as .pptx or .xlsx).
The coauthoring functionality is not available for .doc files (the Microsoft Word 93-2007 format), .rtf files, templates (including modern format .dotx, .potx), or other formats. Additionally, macro-enabled PowerPoint presentations (.pptm) or Word documents (.dotm) do not support AutoSave and thus can't be coauthored.
Depending upon the format your file is in, the easiest solution may be to save a new copy of the file, in the modern format, and work from that new copy.
You don't have edit permissions for this file
If you do not have edit permission for the file, the coauthoring functionality is not available. Ask the owner of the file to grant you edit permissions.
Other features that can’t be used with the coauthoring functionality
The coauthoring functionality is not available if the document is marked as final or if it includes the following:
Information Rights Management or Digital Rights Management
The coauthoring functionality is not available if the document is a master document or a subdocument, or if the Store random numbers to improve Combine accuracy option is not selected in File > Options > Trust Center > Trust Center Settings > Privacy Options.