Fix for this issue is now available in the latest update of InDesign 2020 – that is, InDesign 15.0.1
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 face any problem with the updation process.
Adobe InDesign Team
An error occurred while saving the commentChris commented
This problem just started for me. It says it's overwriting the PDF, but does not. It does overwrite when a copy with the same name is physically dragged into the folder. Adding this step to the process is NOT ideal.
I am running 15.0.1