Hi
@Kormoran thank you for your report. Firstly let me reassure you your quests are progressing normally. It happens sometimes that a player needs to take certain specific game actions in order to trigger the next quest in the sequence. I cannot say for sure what those game actions might be in your particular situation, but provided you are playing normally (so acquiring provinces, doing research, building your city and so on...) the next quest should trigger for you whenever the conditions are met for it to do so.
Please continue to play normally for now and let us know if your next story quest does not appear within a few more days.