Fuel efficient, reliable Mid size luxury SUV

Okay, you list priorities as gas mileage, interior styling, reliabilty and durablity and a price of $45K, 2 years old, and 50,000 max.

To me there is one option and one option only. The Lexus RX 450h Hybrid. It checks all the boxes, although interior styling is quite subjective as you either like it or not. You can find then for less than $45K near you on TruCar, well under 50,000 miles and two years old. They are very reliable by every measure and EPA gas mileage is 31 city, 28 highway, 30 overall. Near me there are 13 of them, and 9 are under your price point.

If you don't like Lexus are are willing to take a hit on reliablity (although not as bad as it used to be) you could get another Audi Q5 or BMW X3 as they drive differently, have different interiors, and don't offer hybrid motors.

While I own a Buick Envision and I am perfectly happy with it (2018) after one year and almost 19,000 miles, I don't think it is luxurous enough for you considering what you have. I bought it because it is reliable (it had been made for 4 years when I bought mine with proven powertrain parts that were about 7 years old in 2018 and is a light hybrid where the engine turns off at stop lights and signs).

I would avoid anything else as the reliablity suffers (I would not consider them).

Agreed on Lexus RX series. If fuel efficiency is somewhat flexible and you can get a better deal on the RX350 then it might be worth it over the 450h.

For a second option in that category a Mazda CX-5 Premium with the turbo is also an excellent vehicle for the above mentioned reasons.

The third choice is going to sound crazy, so bear with me. I was in the market for a Mercedes GLA250 BMW X1 or Lexus NX. I decided to check out some other options as well from Nissan, Honda and Toyota. The driving performance of the HRV and RAV-4 were terrible in my opinion. Then I test drove the car I ended up buying, a Hyundai Kona 1.6T Ultimate. They've made great progress by poaching BMW and VW top talent and it shows with the Kona. Its wheels are wider than the competition and has a zippy 7sp DCT that blows awat the other Japs. In your case, I would at least recommend test driving a fully loaded Sante Fe 2.0T Ultimate. It's a great car for the money and you'll get safety and tech features that aren't surpassed. As long as you don't care about the badge. For me, it was a second car and the MB, BMW and Lexus dealerships were too far away (min 2 hours drive to 6 hours drive) to risk their dubious reliability (except Lexus but that dealership is furthest away at 6 hours). The Hyundai has been good choice in retrospect. They don't make the Sante Fe "Sport" anymore but that's a good option for something a but smaller than the regular Santa Fe.

Let us know what you decide and how it goes.