SUMMARY
It is not possible to access or edit Software Sources through the Discover interface.
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STEPS TO REPRODUCE
1. do a distribution upgrade
2. Start Discover from the Task Bask or start menu
3. click settings (everything on this page works)
4. select software sources 

OBSERVED RESULT
- this launches a password window which does not accept the correct password. Upon entering a new window is spawned with the message:

Permission denied.
Possibly incorrect password, please try again.
On some systems, you need to be in a special group (often: wheel) to use this program.

Command: /usr/bin/software-properties-qt

EXPECTED RESULT
That the software sources window would appear as it did prior to the upgrade.

SOFTWARE/OS VERSIONS

Operating System: Kubuntu 22.04
KDE Plasma Version: 5.24.4
KDE Frameworks Version: 5.93.0
Qt Version: 5.15.3
Kernel Version: 5.15.0-27-generic (64-bit)
Graphics Platform: X11
Processors: 16 × AMD Ryzen 7 5800X 8-Core Processor
Memory: 15.5 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 1080 Ti/PCIe/SSE2

ADDITIONAL INFORMATION
The command:  sudo -H software-properties-kde, opens the Software Sources window.