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

No

While the meaning and spelling of "mexendo" are identical in both dialects, there is a significant difference in typical usage and grammar. In Brazilian Portuguese, the gerund (mexendo) is the standard way to express an ongoing or continuous action. In Continental Portuguese, the standard and natural way to express this is by using the preposition a followed by the infinitive (a mexer). While a Portuguese person would understand "mexendo," they would rarely use it in natural, everyday speech.

Brazilian Portuguese Examples (Using the Gerund)

1. Estou mexendo no meu celular. (I am messing with my cell phone.)
2. Ela está mexendo o açúcar no café. (She is stirring the sugar in the coffee.)
3. Pare de mexer nas minhas coisas! (Stop touching my things!)
4. Ele estava mexendo na gaveta sem ninguém ver. (He was rummaging through the drawer without anyone seeing.)
5. Você está mexendo com a minha paciência. (You are messing with my patience.)

Continental Portuguese Examples (Using a + Infinitive)

1. Estou a mexer no meu telemóvel. (I am messing with my mobile phone.)
2. Ela está a mexer o açúcar no café. (She is stirring the sugar in the coffee.)
3. Para de mexer nas minhas coisas! (Stop touching my things!)
4. Ele estava a mexer na gaveta sem ninguém ver. (He was rummaging through the drawer without anyone seeing.)
5. Estás a mexer com a minha paciência. (You are messing with my patience.)