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

Yes

The word mas is identical in both Brazilian and Continental Portuguese regarding its spelling, grammatical function, and meaning (it is an adversative conjunction meaning "but"). There are no differences in how the word is used to connect ideas or its role in a sentence. The only difference is pronunciation: in Brazil, the "a" is typically pronounced with an open vowel [ma̠s], whereas in Portugal, the vowel sound is often more closed or slightly reduced depending on the speaker's regional accent.

Brazilian Portuguese Examples

1. Eu queria sair, mas está chovendo muito. (I wanted to go out, but it is raining a lot.)
2. O ônibus atrasou, mas eu cheguei na hora. (The bus was late, but I arrived on time.)
3. Ele é muito legal, mas às vezes é um pouco chato. (He is very nice, but sometimes he is a bit annoying.)
4. Eu gosto de estudar, mas prefiro descansar. (I like to study, but I prefer to rest.)
5. A comida estava ótima, mas faltou sal. (The food was great, but salt was missing.)

Continental Portuguese Examples

1. Eu queria sair, mas está a chover muito. (I wanted to go out, but it is raining a lot.)
2. O autocarro atrasou, mas eu cheguei à hora. (The bus was late, but I arrived on time.)
3. Ele é muito giro, mas às vezes é um bocado chato. (He is very nice, but sometimes he is a bit annoying.)
4. Eu gosto de estudar, mas prefiro descansar. (I like to study, but I prefer to rest.)
5. A comida estava ótima, mas faltou sal. (The food was great, but salt was missing.)