I suspect existing alliance agreements are in place. For example the ITA website is listing the Air France lounge in Frankfurt.
From what I understand:
- Miles&More and Volare are working together now until Volare is removed at the end of the year
- codeshare flights are available from February 25th to purchase
- with the start of the NS25 season flight schedule integration starts with ITA joining Lufthansa Group in Frankfurt and Munich, presumably ITA will integrate with Lufthansa Group at other airports as well
- April 30th ITA leaves SkyTeam officially
-at some point before 2027 excluded ITA joins Star Alliance