I have, when I needed a break on a long trip. I am over six feet and so is my son, but my wife is short, so I sit behind her. It was very comfortable back there, but one of the things that I noticed when evaluating the car before I bought it, was the lack of headroom in the rear seats if you get the sunroof. You lose over 2inches of headroom in the rear, which makes it very uncomfortable if you are tall. So I did not get the sunroof, and as long as the front seat passengers are not very tall, it is very nice back there.
I never sat in my back seat as a passenger, although I did ride in the front seat the few times the Spousal Unit drove my Macan. Probably sat in the back seat while it was parked, just to see what it felt like. The kid sat in the back seat regularly. He liked it. He's 12 now (!), taller than I am, & rides in the front, unless all 3 of us are together.
I sat in the back seat for about 10 minutes in the dealership and went through email on my phone. It was tolerable. I also moved the front seat to a position I would have to have it in IF someone was behind me. Then I sat in that. That also was tolerable but I wouldn't want to do that for more than half an hour.
No. Back seat is for my kids. I am the only one that drives my Macan. BTW, regarding losing over 2inches of headroom in the rear if you have sunroof I would never order a Macan without it. Again, the rear is for my kids and the car is for me to enjoy and I wouldn't as much if I didn't have sunroof.
Personally, being 6'3" tall I am not comfortable back there so no I don't sit back there. My wife on the other hand is 5'8" so it isn't to bad for her. Since our sons are grown and gone we rarely use it though except to clean.
I have never sat in the back for any amount of time, but my daughter is 6'0" and she says it is fine. Mine has the sunroof and she says the headroom is still fine for her. We are going on a 1,000 mile road trip (one-way) next month, so we will see how it is on a long trip.
As the OP I want to throw in an additional question. When I ordered the car I asked for a ski bag. The idea was to put the center section down between the rear seats and slide the skis in there. Has anybody else ever done this? Would this constrain the back seat use to be impossible? The bag got recalled because of less than German quality but I still have it as new.