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

Yes

The only difference between "muitas" in Brazilian Portuguese and Continental Portuguese is the pronunciation. In Brazil, the vowels are typically more "open" and clearly articulated. In Portugal, the vowels (especially unstressed ones) tend to be more "closed" or reduced, which can make the word sound more clipped or subtle to a non-native speaker. The spelling, grammar, and meaning remain identical in both varieties.

Brazilian Portuguese Examples

1. Eu tenho muitas amigas na escola. (I have many friends at school.)
2. Ele fez muitas perguntas durante a aula. (He asked many questions during class.)
3. Tem muitas frutas na geladeira. (There are many fruits in the fridge.)
4. Nós vimos muitas pessoas no ônibus. (We saw many people on the bus.)
5. Ela está fazendo muitas coisas hoje. (She is doing many things today.)

Continental Portuguese Examples

1. Eu tenho muitas amigas na escola. (I have many friends at school.)
2. Ele fez muitas perguntas durante a aula. (He asked many questions during class.)
3. Há muitas frutas no frigorífico. (There are many fruits in the fridge.)
4. Nós vimos muitas pessoas no autocarro. (We saw many people on the bus.)
5. Ela está a fazer muitas coisas hoje. (She is doing many things today.)