This cracked me up today. I was in the process of cleaning up and refactoring our/my ArcGIs Pro SDK code and while searching for an answer on good old google I received this response.
"Developing a console application or other non-UI executable with the ArcGIS Pro SDK is not supported. The SDK is designed to create add-ins that run within the ArcGIS Pro application, not as standalone processes. Accessing the ArcGIS Pro API, including GIS data models and the application's core functionality, requires a connection to the main ArcGIS Pro UI and its underlying message loop"
Haha. I wish I would have seen this a decade ago when I started writing our geodatabase interface. It would have motivated the **bleep** out of me. The fastest way to motivate an engineer is to tell them it can't be done.
Regardless, we already had a standalone application in ArcObjects to interact with geodatabases since we went to 64 bit and it stayed at 32. The only way I could figure to keep talking to ESRI stuff was through a stanalone exe and IPC. When Pro came out we just stuck to the same thing since we could use the same base code in our application and just write another Pro executable. We launch whichever one the user has a license for. So here I am a decade later, after writing my own message pump on the MCT and throwing responses back and forth over the fence between our photogrammetric package and geoDBs without incident just to find out I shouldn't do that. Hardy har!
