Update as of 8/14 for those who are interested: the wife and I landed in FRA and had to present our U.S. marriage certificate at border control (wife is a U.S, I’m a German citizen). The document was not legalized with an apostille but no issues whatsoever. Right before baggage claim the COVID test team greeted us and asked if we had taken a test before departure. We showed them the Walgreens test result that was dated 8/12, no issues either. Grabbed our bags and had to show the test result one more time before exiting the testing area. No mandatory test or quarantine needed.

i specifically asked if we had to submit the test result to the authorities but only got shrugs in response. Based on that I won’t waste my time making phone calls — if there was such a requirement, they would’ve told us there and then.