Hi Patrizia and welcome to our community. South Africa is on Italy's List E, and Italy currently isn't open to tourism for travelers from those countries. Check the list here16 to see if you qualify under one of the exempted categories.
Pfizer vaccines are recognized by the European Medicines Agency, and therefore they are valid in Italy. However, the question is whether your vaccination certificate from South Africa will be recognized as an equivalent for a super green pass once inside the country, for accessing venues such as restaurants and hotels. This is less clear. On the Italian government's green pass website, it specifies that certificates from Canada, Japan, Israel, Northern Ireland, the UK and the US are valid equivalents (source here6, Italian only). That inclines me to think your certificate wouldn't be valid. But, you can check with the Italian health ministry by calling their Covid hotline2 at +39 0232008345 - +39 0283905385 so they can give you a definitive answer.