Transit on the outbound will be to another Schengen country from the U.S. via Frankfurt. On the return, it says rule does not apply when transiting to a non-Schengen country (U.S.), so that is quite clear.

I looked at the page you mention above as well as https://www.schengenvisainfo.com/new...-from-march-3/ ("Germany accepts all vaccination certificates that prove that the holder that been fully vaccinated with one of the doses of the approved vaccine in the last 270 days.") and Lufthansa website, which took me to the Paul Ehrlich Institute and again to a German only version of the entry rules (there is a mention on page 2 of "no more than 270 days have passed since the second single vaccination"). So it appears there is a risk of a double vaccinated passenger who just passed 270 days since 2nd dose not being allowed to travel even to transit? Just trying to understand their bottom line.

Lufthansa https://www.lufthansa.com/us/en/long...ns-at-a-glance lists the exceptions very clearly, so I believe as a dual U.S./ EU citizen traveling with my U.S. citizen spouse with marriage certificate in hand we are covered under the last exception anyway and don't have to rush now to get a booster shot just for a 2-hour transit through Frankfurt. I can see this being a nightmare this summer when many not-so-frequent flyers travel if not updated or communicated very clearly!

(From LH page) Entry restrictions do not apply to:
-German citizens and their immediate family members traveling with them;
-German legal residents and their unmarried partners with proof;
-Transit travelers who stay in the airport transit area;
-EU permanent residents or long-term visa holders returning home;
-Citizens of the EU, Liechtenstein, Switzerland, Norway, and Iceland and their spouse, unmarried minor children, and parents of minors.