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 commentElinor Zach commented
I'm encountering the same issue - there's a second line indent that shouldn't occur as per my settings.
All files created in previous InDesign versions and opened in the 2020 version have this bug.
I'm using InDesign 2020 (Hebrew support) on Mac OS Catalina