Fix for this issue is now available in the latest update of InDesign 2020 – that is, InDesign 15.1.2
In the Creative Cloud Desktop application, click on the Updates section on the left. You should be able to see the Update available for InDesign. Please update your InDesign application to this version to try out the fix.
Let us know in the comments section if you still face this problem.
Adobe InDesign Team
An error occurred while saving the commentHelen commented
We are having the same problem in our office with PDFs and Indesign files when we try to save overwrite. We have been changing the name of the file and saving and then trying to delete the old file and it says its still in use! Any help would be very welcome! It is slowing our work pace down.