How can a person have a sound basis in logic or fact? Only an argument or theory (or similar) can. You can have a valid theory or a valid argument, but not a valid person.

I know where it comes from: from Italian via Maltese – “persuna valida”. You can’t use it in English, though, and I strongly suspect that even in Maltese it’s rubbish language.

Valid: (of an argument or point) having a sound basis in logic or fact; reasonable or cogent.

I thought it could be used as an adjective for a person too.

All individuals are valid. That is the basis of fundamental human rights (and Christianity). I’d love to know where this “valid person” thing came from.