Learn Portuguese (Portugal): O vigilante vai barrar o convidado VIP. - The security guard is going to block the VIP guest.

No, this is a false friend! In Portuguese, a vigilante is simply a professional security guard, watchman, or invigilator. The English concept of a vigilante (someone taking the law into their own hands) is usually translated as a justiceiro.

When should I use barrar instead of bloquear for the verb to block?

Barrar is used specifically when denying physical entry, access, or passage, like bouncing someone from a club or barring them at the door. If you are talking about blocking a road, freezing a bank account, or blocking someone on social media, you would generally use bloquear.

How is the English loanword VIP pronounced and used here?

In Portugal, VIP is generally pronounced as a single word, sounding like vipe, rather than spelling out the letters. It acts as an invariable adjective, which is why it comes immediately after the noun it describes (convidado).

How could we use the current lesson's grammar to say The security guard is going to block whoever it is?

You can replace the specific guest with seja quem for (whoever it may be). The sentence becomes O vigilante vai barrar seja quem for. This uses the verb ser in the subjunctive to express that the guard will block absolutely anyone who tries to enter.