The Italian government extended the requirement of wearing an FFP2 (N95) mask until September 30, 2022 on all forms of public transport except airplanes.
See the health ministry press release (in Italian) here.
This includes wearing a mask on inter-regional, Intercity and high-speed Frecce trains.
This extension was included in a transport decree, not a health ministry decree (Article 11).
Regarding the exclusion of airplanes from this ordinance, the Italian family minister said the government is still evaluating whether to extend the mandate. However, currently in the official ordinance airplanes are excluded from the extension.
A bit of practical advice:
What's written in Italian government ordinances isn't always uniformly applied by workers on the ground. Despite the fact that airplanes are technically excluded from this mandate at the moment, smart travelers should have the FFP2 masks ready with them at all times while flying into, out of, and within Italy, until this issue is further clarified.