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

No

While the fundamental meaning of "sócio" (business partner or club member) is identical in both dialects, there are differences in the grammar surrounding its use and in the typical usage of related professional terminology. In Brazilian Portuguese, the definite article is frequently omitted before possessive pronouns (e.g., "meu sócio"), whereas in Continental Portuguese, it is standard to include it (e.g., "o meu sócio"). Additionally, when referring to the managing partner of a company, Brazilians typically use the term "sócio-administrador," while the standard term in Portugal is "sócio-gerente."

Brazilian Portuguese Examples

1. Ele é meu sócio na nova empresa. (He is my partner in the new company.)
2. Preciso falar com o sócio-administrador. (I need to speak with the managing partner.)
3. Tornei-me sócio do clube de tênis. (I became a member of the tennis club.)
4. Procurei meu sócio para discutir o contrato. (I looked for my partner to discuss the contract.)
5. Meu sócio viajou ontem. (My partner traveled yesterday.)

Continental Portuguese Examples

1. Ele é o meu sócio na nova empresa. (He is my partner in the new company.)
2. Preciso falar com o sócio-gerente. (I need to speak with the managing partner.)
3. Tornei-me sócio do clube de ténis. (I became a member of the tennis club.)
4. Procurei o meu sócio para discutir o contrato. (I looked for my partner to discuss the contract.)
5. O meu sócio viajou ontem. (My partner traveled yesterday.)