You can do that via ÖBB (using these steps) as soon as the Italian summer timetable has finally arrived. Timetable updates are twice a week early Tuesday and Friday morning. It's still 3 months in advance so there's no rush to get these reservations.

Thx! Do you know when that’s possible?

It should not take very long anymore. Trenitalia have already published the summer timetable for long distance trains (valid from 12 June) on their own website. Regional trains will probably only appear next month.

When is it regional or long distance?

In Italy, long distance trains are the ones that need a reservation.

Please also check the country information.

Certainly R→ Anc has also enough and not that much slower RV trains. Its a nice ride as it crosses that booth of IT via the Apennines mountains, thus its also quite slow.

IF you had also done a break in Frienze-another oso famous touristy town, it would also have bee more possible to go via UNres- regional treni on both sectors.

Thanks, so I have to be a little more patient, an I will try to find a RV train to Ancona.