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

Yes

The meaning, spelling, and grammar of "mensal" are identical in both Brazilian and Continental Portuguese. The difference lies solely in pronunciation. In Brazilian Portuguese, the vowels are more open and the rhythm is syllable-timed, making the word sound more melodic. In Continental Portuguese, unstressed vowels are more closed or even reduced (often sounding almost "swallowed"), and the rhythm is stress-timed, which makes the pronunciation sound more "clipped."

Brazilian Portuguese Examples:

1. O pagamento mensal vence no dia cinco. (The monthly payment is due on the fifth.)
2. Eu tenho uma assinatura mensal de streaming. (I have a monthly streaming subscription.)
3. O valor da mensalidade subiu bastante. (The monthly fee went up a lot.)
4. Ele faz um depósito mensal na poupança. (He makes a monthly deposit into his savings.)
5. O relatório mensal está pronto para revisão. (The monthly report is ready for review.)

Continental Portuguese Examples:

1. A fatura mensal chegou hoje pelo correio. (The monthly bill arrived today by mail.)
2. Tenho uma subscrição mensal de uma revista. (I have a monthly subscription to a magazine.)
3. A quota mensal do clube é cara. (The monthly fee for the club is expensive.)
4. O vencimento mensal é sempre o dia dez. (The monthly due date is always the tenth.)
5. Fiz o pagamento mensal do seguro. (I made the monthly insurance payment.)