Is the word dessa the same in Brazilian and European Portuguese?

No

While the spelling and core definition (the contraction of the preposition de and the demonstrative pronoun essa) are identical, there are differences in pronunciation and typical usage.

Pronunciation: In Brazilian Portuguese, the vowels are generally more open and the "e" in the contraction is clearly articulated. In European Portuguese, unstressed vowels are often reduced or even swallowed, making the word sound more like "d'essa."

Usage: There is a notable difference in how much "ground" the word covers. In Brazilian Portuguese, "dessa" is frequently used to refer to abstract topics or ideas that were just mentioned in conversation. In European Portuguese, there is a stricter distinction: "dessa" is used for things or topics physically or contextually close to the listener, while "disso" (the contraction of de + isso) is the standard for referring to abstract concepts or things previously mentioned.

Brazilian Portuguese Examples

1. Não gosto dessa cor. (I don't like this color.)
2. O que você acha dessa ideia? (What do you think of this idea?)
3. Tire a mão dessa mesa. (Take your hand off that table.)
4. Eu não entendo dessa maneira. (I don't understand it this way.)
5. Não fale dessa forma. (Don't speak in that way.)

European Portuguese Examples

1. Não gosto dessa cor. (I don't like that color.)
2. O que achas disso? (What do you think of that?)
3. Tira a mão dessa mesa. (Take your hand off that table.)
4. Eu não entendo disso. (I don't understand that.)
5. Não fales dessa forma. (Don't speak in that way.)