European Portuguese (pt-pt) and Brazilian Portuguese (pt-br) have the same base (Portuguese), but evolved in different ways over the centuries. (Portuguese people tend to prefer English, if there’s only pt-br available, although we understand almost 100% of pt-br. This is not the same for Brazilians who have more trouble understanding European Portuguese - mainly spoken pt-pt).
Brazilian Portuguese, kept some rules and similarities to 16th-18th century Portuguese and evolved in a different direction.
This differences are always really hard to explain to foreigners (non portuguese speakers). My wife is Polish and when we met, she used to say European Portuguese sounded like a weird Russian dialect and that PT-BR was easier to understand and learn. (they kind of sing the words and separate each word more clearly, than we do).
I’d say a good comparison would be French from France vs French from Canada (Français Québécois). My brain melted when I first tried to figure out what “Clavardage” meant, or expressions like “Piquer une fouille” - (Quoi ?) lol.
Here’s some videos regarding the differences of pt-pt / pt-br:
Small precision regarding the use of “1st / 3rd person” (Tu / Você). In Portugal besides the example in the video, when in a context of a company addressing it’s customers, it highly depends on target demographics and product. So in a game like Infinity:Battlescape, 1st person (tu) is the norm, while “Life insurance” would use the 3rd person (você) and be much more formal. Again, similar to FR.