Hi,
Based on your description, you're Office 365 and this feature is now retired on Office 365.
As the
article said:
If you’re using Office 365 subscription this feature is no longer available. All new files checked-out in Office 365 will check-out using the Office Document Cache. This change enables offline editing of checked-out files and allows you to edit your
checked-out files from more than one machine.
If you have a file checked-out to your local server drafts folder and have lost access to this feature you can still retrieve any changes that were not checked-in to SharePoint. You will need to open the local copy of the file from the Server Drafts location
to copy any changes you have made, then paste these changes into the checked-out file from SharePoint. Once done, you can check-in the file as normal.
Hope the information is helpful.
Regards,
Emi
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