Only the historical core of the town (the little skin tag west of Via Santa Chiara) is closed to non resident traffic. Before you enter you'd see the ZTL sign below:
https://maps.app.goo.gl/cFeF3uDwGNKnpfkh9
I was there in 2022 and parked on the street not far from the above at a metered parking zone. Remember that if you see parking stalls blue stripes on the ground it means pay parking (in that case you usually pay at a machine then place the receipt on the dashboard). If you intend to get accommodations inside the historical core, you'll probably have to park outside and walk in.
There are buses that you can use to reach the town, but they are not frequent especially on weekends, therefore without a rental car you'd be severely limited on your ability to visit places nearby.
PS: Pitigliano is in the Province of "Grosseto". Tuscany is the Region (the Province of Grosseto is one of the 10 provinces in the Tuscany region)