Windows 11, Indesign 20.1
Steps to reproduce:
1. With at least one PDF export profile present, export an INDD to PDF
2. In the export dialog, change something on the settings, like checkmarking "Create Acrobat layers", given it's not marked already. The export profile would then become marked as "(modified)".
3. Select the unmodified profile again, to remove the previously set checkmark.
4. Now change the settings "Pages" from "All" to "Range". The export profile is now NOT marked as modified.

Conclusion: if you want to reset the export from Range to All, you cannot do that by simply selecting any profile, you have to do it manually. Thats illogical.