As a Brazilian - Pix was a pleasant surprise, especially in that for once it feels like we're not lagging behind. It's convenient, free, instant transfers across banks. You can also easily create or programmatically generate QR codes or pastable codes with preset receivers and amounts. Great UX all around, and it quickly became the de-facto standard in how people send money.
It's technically quite impressive - it's a large scale thing and it works really well. I can think of maybe one or two times in these years where I saw downtime, and in both cases it was working again after a few minutes. The usual experience with the government building technical solutions is to have something that makes little sense, is slow, and goes down frequently with even the most predictable usage peaks, but with Pix they really seem to have nailed it.
It does feel a bit weird to have so many payments go through the government's systems, and it definitely feels like it puts them in a position of having more information than they should. There's a lot of Orwellian surveillance potential there, as any transfers are necessarily tied to both users' real identities. I don't think there's a realistic way around this, though.
Another concern is that people can expose some of their information without necessarily being aware of it. You can register e.g. emails and phone numbers as Pix "keys", and then anyone can initiate a transfer to those keys and your full name will pop up so you can confirm or cancel the transfer. I've seen some clever advice around this - "When using a carpooling app (often details are arranged off the platform using WhatsApp), put the driver's phone number on Pix. If a name comes up and it doesn't match the name or gender of the driver's profile, something is up". Obviously though there's potential for misuse and I'm sure the vast majority of people don't think about this when registering their Pix keys. You can, however, just use randomly generated uuids as keys as well, a different one for each transaction if you so desire, so this one can be a non-issue with more awareness.
Overall though it's a very convenient thing which works surprisingly well, and the downsides are theoretical at this point. IMO it's a rare case of our government nailing something.