Pets on Public Transport?

Whilst you asked about personal experience - which I don't have - I can share a useful article about the legal and regulatory situation. As with so much in Portugal, the law is pretty clear; but some local interpretation is to be expected.

https://www.amt-autoridade.pt/consumidor/informa%C3%A7%C3%A3o-ao-consumidor/viajar-nos-transportes-p%C3%BAblicos-com-animais-de-companhia/

It's in PT, but is an official source, and has the benefit of containing links to the relevant legislation.

Hey, Carl.

Konni and I looked into this because we're bringing our cats with us when we arrive in June.

On the trains, at least, you can have small animals as long as they are in some kind of carrier. So, I can say for sure that cats in carriers is fine on CP.

We're going to be taking them with us on the Porto Metro too when we arrive in the airport and take the Metro to our place in VNG.

Here's the specific case of trains and pets: https://www.cp.pt/passageiros/en/how-to-travel/Useful-information/travelling-with-pets

They're allowed on the Metro as long as they're in a carrier or muzzled (for larger dogs) - we've taken our dog in a carrier on planes, trains, the Metro in Porto, and automobiles (Ubers). Only had one instance of an Uber driver refusing to take us, but the real issue seemed to be that his trunk/boot was small and taken up with a car seat, and our suitcase was probably too big to fit.

So, definitely dog friendly! Will update after we take him in a bus, (but I think they follow the same rules) though it won't be anytime soon - the streets are very narrow and winding here.