Just got back from a trip last week. I averaged ~$1100 to $1USD on all my card transactions. It's roughly what I got from exchanging cash at an official exchange place. From looking at blue rate, it wasn't far off so I didn't go through the hassle of finding an informal exchanger but in Buenos Aires, they're literally everywhere. I stayed near Galeria Pacifica for a couple of days and on the pedestrian street outside, there were 2-3 people at every corner and more in between.

Shops and restaurants in tourist areas will take dollars and Euros sometimes, they have signs on their doors. I was also in Bariloche where a lot of places took dollars as well and there were money exchangers on every corner.

I paid in pesos everywhere, some places put dollar conversions on the receipt as well that looked better than the official rate. But when I asked once, they said it wasn't correct so I paid in pesos. It wasn't a huge difference, a few %.

I was worried before going because I knew someone who went a year ago and they had to pay for everything in cash because the blue rate was 2x better than official rate. But things have stabilized significantly since then it seems.