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

No

While the fundamental meaning of "sentar" (to sit) is the same in both dialects, there are significant differences in usage and grammar, specifically regarding the use of reflexive pronouns.

In Brazilian Portuguese (BP), it is very common to use "sentar" intransitively (without a reflexive pronoun) in casual speech, or to place the reflexive pronoun before the verb (e.g., "Eu me sentei"). In Continental Portuguese (PT-PT), the verb is almost always used reflexively (sentar-se) when referring to the act of sitting oneself down, and the pronoun is placed after the verb (e.g., "Eu sentei-me"). Additionally, there are differences in vocabulary for other parts of the sentence, such as the use of "com a gente" in Brazil versus "connosco" in Portugal.

Brazilian Portuguese Examples

1. Pode sentar aqui. (You can sit here.)
2. Eu me sentei no sofá para descansar. (I sat on the sofa to rest.)
3. A criança não quer sentar. (The child doesn't want to sit down.)
4. Vem sentar com a gente! (Come sit with us!)
5. Ele se sentou na cadeira de um jeito estranho. (He sat in the chair in a strange way.)

Continental Portuguese Examples

1. Pode sentar-se aqui. (You can sit here.)
2. Eu sentei-me no sofá para descansar. (I sat on the sofa to rest.)
3. A criança não quer sentar-se. (The child doesn't want to sit down.)
4. Vem sentar-te connosco! (Come sit with us!)
5. Ele sentou-se na cadeira de uma maneira estranha. (He sat in the chair in a strange way.)