After several hours (4+) trying every combination described here and elsewhere, what ultimately worked was uninstalling ALL Adobe software and starting from scratch.
1. Uninstall any and all Adobe software:
- Adobe AIR
- Adobe Flash
- DPS App Builder
- Adobe Creative Cloud
- Adobe InDesign
- Adobe Photoshop
- Adobe Illustrator
- Previous downloads of installers
- Etc.
2. Clear all system and user caches, preferences, bootcaches, kextcache, etc.and reboot (whether necessary or not; just for good measure).
3. Run the Adobe Creative Cloud Cleaner Tool to confirm everything was removed.
4. Reboot (whether necessary or not; just for good measure).
5. Confirm no Adobe affiliated process is running in the Activity Monitor (or Task/Process Viewer in Windows).
6. Download a new clean installer for Adobe Creative Cloud.
7. Cross fingers.
8. Install Adobe InDesign.
9. Reboot (again, just because).
10. Install Adobe InDesign updates (which should download the necessary DPS tools too).
After all this, the Folio Builder finally appeared and began working again for my computer.