Can I use a Global Pass to travel from Interlaken to Civitavecchia Italy?
Yes, but you will probably need to make additional seat reservations for Italian EC, IC, and Freccia trains. Using all regional Italian trains would be rather tortuous and time consuming.
You WILL need to make seat reservations with a fee for all Italian trains except the Regional trains. Regional trains are open seating - no reservation.
Yes, you can use a Eurail Global Pass to travel by train from Interlaken to Civitavecchia.
You will, as the others say, need to buy reservations for all Italian non-regional trains.
The elephant-in-the-corner is: Is this the best way to pay for travel?
The answer is probably not. Buying Italian tickets in advance is probably cheaper. Read here: https://www.seat61.com/Italy-trains.htm