After communication with KOMBIT it has become clear, that there is no documentation as of for how to test sending Digital Post from OS2valghalla through the https://digitaliseringskataloget.dk/integration/sf1601 integration to a test user in the Digital Post test environment.
However KOMBIT tells us we can use one test person from the test data available in the https://digitaliseringskataloget.dk/integration/sf1520 test environment to send Digital Post to.
That is the person with this test CPR number: 190283-0000