Launch Fantastical with a x-callback-url
I have a Morning Routing project in Omnifocus which includes an entry to check Fantastical. In the Omnifocus item's note, I have a link to open Fantastical.
x-fantastical3://show/calendar
This is possible thanks to x-callback-url links:
Using x-callback-url’s source apps can launch other apps passing data and context information, and also provide parameters instructing the target app to return data and control back to the source app after executing an action.