SUMMARY
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***


STEPS TO REPRODUCE
1. Enable startup sound / Notification theme (Settings > Colors & Themes > System Sounds
2. Verify startup sound is enabled (Settings > Notifications > Configure > Plasma Workspace > Login)
3. Preview startup sound
4. Reboot laptop / computer
5. Startup / Login sound should play but does not

OBSERVED RESULT
No startup / login sound

EXPECTED RESULT
Selected startup / login sound should play upon logging in after reboot

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 6.0.0
KDE Frameworks Version: 6.0.0 
Qt Version: 6.6.2

ADDITIONAL INFORMATION
There was a problem a few years back with Plasma where sound was muted during the startup / login process, but was automatically un-muted after the desktop loaded. The startup / login sound was playing, but was basically muted. Not sure if that is the case this time. Previous workarounds did not resolve this issue for me.