And because the same card can be both. At least here in Brazil, most bank cards have multiple uses (credit, debit, ATM) in the same card. AFAIK, they're separate applications within the same chip, and the terminal has to select which one to use before starting.

The BIN will tell you which bank was the issuer and which class of card you have, like standard or premium, though most readers probably don't take that into account beyond the card scheme and card type associated with the range that the individual BIN is in. Many banks will have multiple BINs for the same card type if they are large.

Credit / online debit / offline debit usually get different ranges. The reader gets a list of the ranges when it updates and they don't change super often. Offline readers can be configured to reject cards with a number in an online only range.

Nope, even this is identical. These days the difference between a debit/credit card is pretty much aesthetic, from a transaction processing perspective there generally isn’t any actual differences. Differences that people see today are most artificial for the purpose of justifying extra fees, or higher interchange based an entirely arbitrary factor that has zero correlation to any risks that appear in the transaction processing and clearing mechanisms.

Basically the only reason anyone really bothers keeping the difference between credit/debit cards around, is as a technical excuse for discrimination and abusive fees. Notably in the EU nobody cares if a debit or credit card is used, because the EU outlawed all the crazy fees and other bullshit, so now there’s no commercial reason to differentiate between the two 99% of the time.