I am searching for dates in July ‘23 - is this perhaps too far ahead?

First it is the Eurail Pass, not Eurorail Pass.

Yes you are too early for this summer, especially for Italy as they are always late sending their schedules.

Castiglion Fiorentino - Florence doesn't need reservations, simply board the train (and add the journey to your app).

Florence - Interlaken West will need 2 reservations (when available) :

- Florence - Milan 10€ Frecciarossa train

- Milan - Switzerland (Brig or Spiez) 11€ EC train

As soon as you're in Switzerland, reservations are optional and a waste of money so don't do them.

At what time does your flight leave Fiumicino Airport ? You might need to leave Interlaken very early. Again it should be 2 reservations :

- Swiss border - Milan

- Milan - Rome

These reservations are best bought on tickets.oebb.at (no booking fee there) but as you can see they're not available yet

Thank you for the reply advisory - ‘Eurail’ Pass NOTED.

Eurail Support has advised me to go by local train from Castiglion Fiorentino to Arezzo - then reserve seats as required on to Interlaken West. 

Return train is now (accommodation adjusted) to be Spiez to Rome ….

I hear you on Interlaken - Rome (airport) to fly timewise. But flight is next day as staying at hotel very close to airport for next day flight so managed thanks

As you say none of the Eurail searches yield a need to reserve seats in Switzerland.

I will check tickets.oebb.at but bit early as you say thanks

Thank you again - learning heaps

To get to Florence, either direct regional train or regional train to Arezzo + IC train to Florence (3€) depending on your schedule.

You're welcome