SUMMARY
Kleopatra does not have anymore an option to set any of all 5 different trust levels from the GPG backend, which in turn implement the RFC-4880 specification.
I have already brought up this topic in Gitlab, where Ingo Klöcker kindly suggested to move the issue here.
I can see his point, and I can agree on making a UI which is simpler to use, but I don't find it particularly wise to make a step back to do so, especially for KDE software. Maybe the old menu could have been moved to an advanced section elsewhere, but that functionality cannot be entirely missing, in my opinion.
Also, the way in which the new functionality has been implemented, basically transforms key trust management into a FSM with forced transitions (forced by which options you can click), which in my case required me to go and look into the actual code to get a clear understanding of what was going on.

OBSERVED RESULT
Kleopatra does not have an option to set key trust level anymore.

EXPECTED RESULT
Kleopatra should reflect GPG behavior, or at least allow for same functionality as GPG, even if layed out differently. A simplified way is welcome, but should reflect backend behavior.

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

ADDITIONAL INFORMATION