singapore-shanghai-hong kong-singapore

Good morning! I have an Italian passport.
I have booked flights from singapore to Shanghai and then from Shanghai to Hong Kong and then back to singapore.
Since that I am staying in Shanghai for less than 72 hours I wanted to know if it is fine to ask for a "72 hours visa exemption” in Shanghai because my third destination is Hong Kong so Shangai would be considered a transit to a third region(Hong Kong).
my question is if Hong Kong is considered to be a third country.
Thank you for the explanation.
Best regards
Filippo Cavalli