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SUMMARY
I was messing around with Kontact in Flatpak to compare feature parity with the older version shipped in Debian 12. The Flatpak tends to take in accounts from Akonadi already in the Debian installation instead of being a completely isolated instance separate from Debian.

STEPS TO REPRODUCE
1. Have Kontact installed from apt on Debian with accounts already set up
2. Install Kontact as a Flatpak
3. Flatpak version recognizes the accounts from the Debian/Apt version and somehow interacts with the Debian Akonadi database
4. Sync, but unsuccessfully. All account info (even from accounts freshly created in the flatpak version) does not sync in the flatpak version and no data populates.

OBSERVED RESULT
Flatpak version of the app is devoid of data for all recognized accounts. All changes and syncing is visible on the Debian version. The Flatpak version is functionally useless when the Debian database exists.

EXPECTED RESULT
The Flatpak should be completely independent of the Debian installation. When installed for the first time, the Flatpak should have no accounts set up and when an account is set up, it should populate accordingly.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Debian 12 with Kernel 6.1.0-18-amd64 (64-bit)
(available in About System)
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8

ADDITIONAL INFORMATION
On Debian version, I set up my Akonadi database to use SQLite instead of MySQL.