mrymsza - I flew direct from the US to Frankfurt and it worked out great!
On Sept 27 I flew DEN to Frankfurt on United Airlines with a layover in Washington DC. The flight from Washington to Frankfurt was almost empty.
I was able to enter Germany with the Declaration of Relationship form (Erklärung zur Beziehung ) and a letter of invitation from my girlfriend. The form is just 2 pages - fill out your contact info and both sign. The letter was 1 or 2 sentences that said I am her boyfriend (Lebenspartner) and that I am invited to stay with her, and the dates.
It was very easy. The passport control agent asked if I had been in Germany before (I have several times) and let me right through:)
It is also required to get a covid-19 test before the flight or within 48 hours of arrival in Germany. I signed up in advance and paid 59 euros. After passport control at the Frankfurt airport I just followed the signs to the testing place there at the airport. The test took a minute or two and they emailed the results.
Now... does anybody know how I can get my girlfriend back to the US?
Can she apply for ESTA online as usual?
Does it work to go outside of the Shengen states for 14 days (Turkey, Croatia, or UK, etc.) and then enter the US?
I have been getting conflicting reports. Several people her have talked about doing the exact same thing but then disappear from the site. Does that mean it works?? I hope so!:)