SUMMARY
Kmail and Korganizer don't show details if akonadi fails to start. In my case:

org.kde.pim.akonadiserver: Starting up the Akonadi Server...
org.kde.pim.akonadiserver: Cluster PG_VERSION is 17 , PostgreSQL server is version  18 , will attempt to upgrade the cluster
org.kde.pim.akonadiserver: Postgres db cluster upgrade failed, Akonadi will fail to start. Sorry.
org.kde.pim.akonadiserver: Database process exited unexpectedly during initial connection!
...

STEPS TO REPRODUCE
1.  Make akonadi fail to start, for example by updgrading posgresql with the old version removed.
2. Start kmail or korganizer, expect:
A required background service is not operations. See FAQ for troubleshooting tips.
3. Click on Details after the 

OBSERVED RESULT
Details button doesn't do anything

EXPECTED RESULT
Show the akonadi start upd failure log.

SOFTWARE/OS VERSIONS
Operating System: Gentoo Linux 2.18
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1
Kernel Version: 6.12.32-gentoo-x86_64 (64-bit)
Graphics Platform: X11
Processors: 16 × 11th Gen Intel® Core™ i9-11900H @ 2.50GHz
Memory: 64 GiB of RAM (62.5 GiB usable)
Graphics Processor 1: Intel® UHD Graphics
Graphics Processor 2: NVIDIA GeForce RTX 3080 Laptop GPU

ADDITIONAL INFORMATION
As far as I remember the failing upgrade from Postgress 16 to 17 gave more use full information.