Is it possible to create a 2nd gen package depending on a external managed package?

Question

So, that's the question, can I make depending on an external managed package (i.e. an app from the app exchange) my second generation package?

Answer 1

Yes, you can. First, see Which Package Dependencies Work with Second-Generation Managed Packages?. The only real limitation here is that a 1GP cannot depend on a 2GP. Dependencies on Unlocked Packages are only "not recommended."

To actually know how do so, read Create Dependencies Between Second-Generation Managed Packages. In summary, you just use the package and version number, like this:

"dependencies": [ 
   {
      "package": "[email protected]"
   }
]