From this page on the Aeroporti di Roma site:
As I read it, Lufthansa and partners, Schengen-based airlines not listed, will check in at T3 but have baggage claim at T1.
So baggage claim will be at T3 for non-stop flights from the U.S. and connections through the U.K. or Ireland, but at T1 for connections through Schengen countries (most of the rest of the Europe). If connecting through a third country, be aware that there could be extra complications with COVID rules.Passengers are advised that as of the 15th of November, check-in operations for Air Baltic, Air Europa, Air France, Iberia, KLM, Luxair, Norwegian, Tap Air Portugal and Wizz Air will be moved from Terminal 3 to Terminal 1.
The latter will be expanded with the opening of a new area available to passengers and represents a further step in the extensive investment programme currently underway to create a new state-of-the-art boarding area, operational by next summer, which will be cutting edge in Europe.
Also from the 15th of November, baggage reclaim for all domestic and Schenghen flights will be transferred from Terminal 3 to Terminal 1, due to renovation work being carried out in Terminal 3.
As I read it, Lufthansa and partners, Schengen-based airlines not listed, will check in at T3 but have baggage claim at T1.