US Citizen – Italy on Covid-tested flight to Croatia, transit Italy to return to the USA?

Italy should allow for a covid vaccine passport within a few weeks, however, to prepare for the worst, I am assuming that current travel restrictions stay enforced through August.

I am planning a trip from JFK/BOS -> FCO -> DBV, then DBV -> FCO -> JFK/BOS.

The JFK/BOS -> FCO segment, if flown via Delta/Alitalia should be allowed, regardless of transit rules, due to it being a covid-tested flight.

FCO -> DBV is allowed with proof of vaccination as a US citizen

FCO -> JFK/BOS is allowed as a US citizen, if a covid test is taken, regardless of vaccination status

Now, my questions:

  1. Is the DBV -> FCO segment allowed, if I do NOT leave the airport? Italian law claims that anyone being in a List D country (USA) within the last 14 days MUST quarantine for 10 days. How does this apply if I previously entered Italy and left?

  2. Would I be allowed to transit Italy to Croatia, if I do NOT leave the airport in Italy? Multiple sources tell me that I can transit Italy by “private means” if I do NOT stay in Italy for more than 36 hours. Does “private means” include an airplane?