Brazil has massive amounts of fraud so credit cards are very inconvenient, card cloning and websites leaking credit card numbers is a huge problem. Banks are super aggressive about blocking cards if they see suspicious transactions. Tap and pay is popular in Brazil as well, but only for physical transactions. For online small purchases PIX is definitely the best option.

PIX (and similar systems like Sweden's Swish/BankID), don't have fraud protection, once you send the money it is gone with no contest possible. But when you send a payment with PIX there is 0 risk your account's money will get highjacked, at most you lose your one transaction.

But PIX is also accepted in many physical places because it has smaller fees, with some stores and informal commerce not accepting cards. I used to work at an IT service provider in Brazil around 2012 and one of the projects my company did was monitoring of those card machines. They actually kept GPS information of the machines and blocked them if they were moved around. Those card machines are surprisingly expensive in Brazil (or at least they used to be).