It depends. Even though it’s not illegal to use a VPN to access Bet365 from anywhere, you’ll need to consult the regulations of the country you’re betting from. This is even the case when you’re trying to access an account that was registered in a country where Bet365 is legal.
Many countries (including Portugal) have banned online gambling and only allow it in brick-and-mortar casinos. While this may not apply to citizens visiting the country and accessing an account they already own in a non-banned country, you’ll still have to verify the laws of the country you travel to ensure it’s not illegal to gamble online.