According to Collins, Britishness is
relating to, denoting, or characteristic of Britain or any of the
natives, citizens, or inhabitants of the United Kingdom
So I guess Portugueseness would be ok.
Alternatively, you can use the "official" latin prefix for things related to Portugual: Luso from the ancient roman province Lusitania.
For example, in French, and in some English books, people speaking Portuguese or Brazilian are called "lusophone".
In this case I'd propose the neologism Lusoness ?
At least one reputable source (the official Translation Bureau of Canada), Termium uses
to translate lusitanité (French) and lusitanidad (Spanish) which is the quality of what is portuguese. (The latest sound a lot like Portugalidade, isn't ?)