Choosing a calendar app

[mekentosj]

Is there a way to choose a different calendar rather then the Apple Calendar?

See this topic:

Opening events in third-party calendar apps

Indeed as @michael.hanson was mentioning, you do need to tell the system that you want Fantastical to be your default calendar app (by going into the Calendar app preferences) as Agenda follows the system default. [17]

PS Love Agenda both for Mac and iOS. Paid for the Premium Features to show my support.

Brilliant to hear, thank you so much!