I've just returned from an impromptu 10 day trip to Jujuy province. I didn't go to Laguna Pozuelos but I asked about road conditions when I was in the nearest towns and the local police told me you can get there in a regular car, driving slowly and carefully, at least at the moment. Again I've never been, but I've also heard that if you are looking for Horned Coot and good concentrations of birds, you also frequently have to do a good bit of driving around once there, as the water levels and bird locations shift around. I did drive from La Quiaca all the way to Santa Victoria Oeste, over Abra Lizoite, to look for Short-tailed Finch, Scribble-tailed Canastero, etc. (Sites for Diademed Sandpiper Plover and other nice birds up there too). All this in the cheapest rental car I could get, which was a Renault Logan. The dirt road is in excellent condition, I had no problems.
Just for anyone else who ends up reading this, I contemplated going to (but didn't, as the communities are still trying to avoid entrance of outsiders due to the pandemic) Santa Ana and Valle Colorado. There is a new road now that connects the two communities (formerly just a trail) so you can now drive from Humahuaca to Santa Ana (2WD), continue down to Valle Colorado (4WD / truck necessary, apparently), then continue down the to Valle Grande and through PN Calilegua (2WD). Looks to be very good birding along the route, but I decided not to try to barge my way into remote communities that are still trying to avoid outsiders / new vectors of contagion.
And on a different note, I would very highly recommend EcoPortal de las Piedras as a destination. While it doesn't have any unique birds that aren't on the standard Los Sosa / El Infiernillo / Yala / Calilegua circuit, it's a stunningly lovely place, tucked off in a corner, very quiet, very friendly, very inviting. They have large private cabins to rent with kitchen facilities, and all you have to do is walk out the door and start birding. There's a lot of hiking to do there, particularly to see the higher elevation species (I don't mind, I prefer hiking to driving for birding). And it's very birdy with a good mix of Chaco and Yungas species. I only saw one new bird in 4 days there (Rothschild's Swift, a long sought species that is scarce and hard to get adequate looks at) but I'd say it is easily one of the best birding sites I've been to in Argentina, and certainly one of my favorite.