I suggest you check oebb.at booking site. Be sure to select eurail/interrail pass as a discount rather than seat only.

Hi, every second Sunday in December there is the yearly timetable change in Europe. So interrail.eu/eurail.com can at the moment sell only to the 10 dec 2022. 

Some trains are on sale, but Trenitalia has not released completely the new timetable. You can check the timetable on trenitalia.com (but like I said, most of the trains are still missing). For the moment it is only possible to book at ticket offices of Trenitalia the reservation. But don’t worry, there are so many trains on the Rome-Firenze route, that reserving the day before is enough. There are even local trains “regionale veloce” on this route, they need some more time, but you don’t need a reservation. 

Reservations for Italian trains online are also possible via Austrian Railways ÖBB, but they do also have not the new Italian timetable yet in their systems. 

Here a tutorial how it works:

Thank you for your best answer.
Then, is that impossible to know when the next timetable will be update on eurail.com?...

Thank you for your best answer.
Then, is that impossible to know when the next timetable will be update on eurail.com?...

At the moment we don't know, but you will read the information in this community for sure.

Do not worry-on this line there are even more as 1 train/HOUR (Not day) so if you can have the slightest amount of flexibilty you will find seats-if more as 1 for a grand Asean family. A few days advacne is enough. Expect times on that day to hardly differ from tomorrow.