In papyrus logs I can see:
I want to see the reasons in game -> City Builder Desk -> City Plan:
Current Level: 1
Percent to Next Level: 100 %
City Upgrade Ineligible: Happiness too low.
Code:
[workshopscript < (000250FE)>]City Upgrade Ineligible Reason: Happiness too low.
[workshopscript < (0009B1AC)>]City Upgrade Ineligible Reason: Not enough plots built or upgraded, levels required: 36, levels found: 26.
[workshopscript < (0009B1DB)>]City Upgrade Ineligible Reason: Not enough time passed.
I want to see the reasons in game -> City Builder Desk -> City Plan:
Current Level: 1
Percent to Next Level: 100 %
City Upgrade Ineligible: Happiness too low.