The issue reported is at Apple’s end.
Hence, Apple is recommending to update macOS to 10.15.x version in order to resolve this issue.
Please update your macOS to Catalina. If you still face this issue in macOS 10.15 do add your comment in this thread.
Adobe InDesign team
An error occurred while saving the commentMatěj Málek commented
Same thing happens to me after connecting Dell U2718Q 4K monitor to my Macbook Pro 13" Retina (2015).
2,7 GHz Inter Core i5
8 GB 1867 MHz DDR3
Inter Iris Graphics 6100 1536 MB
Thank you for your support all this while. The issue is now fixed in the latest update of InDesign.
Please upgrade to the new InDesign 14.0 from your Creative Cloud Application.
If you are unable to see the update yet, click on the menu (three dots) on the top right corner of Creative cloud app and click on “Check for App Updates”.
Let us know if the issue is resolved for you in InDesign 14.0.