Most useful off-road vehicle I’ve ever driven was a lot like this thing: https://www.offroaderie.com/new-models/kawasaki-side-x-side-mule-sx-2036834140399698232475668
Or just a regular sized pickup truck, which I’ve also used for plenty of sites. But honestly I prefer the mules because they hold all the stuff I need for work and can fit through most forest understory. And in the rare chance that you happen to turtle them it’s possible to pull them off/out of whatever they’re stuck on. If you get a giant truck stuck in the mud you’re donezo.
I also took my Toyota Prius to plenty of sites, although I’d never off-road with it when the ground is swampy or sandy it did fine on plenty of rough roads and open fields. I’m sure a Subaru or other small all wheel drive sedan could handle lots of off-road work sites.
Audiobooks+ some other mindless activity shuts my brain off really well. Find a series you love that your library has and pick up a new sudoku or other puzzle app and go to town.
If you’re having trouble finding books I recommend a long sci fi or fantasy series. The Expanse is great, or Dune is also fantastically long. If fantasy is more your style maybe someone can recommend something but I know the wheel of time has a ton of books.
As for mindless things to do while you listen to audiobooks, either find a puzzle game or pick something up to do with your hands that requires few materials and is calming and productive. Here are a few that work for me:
Coloring (you can print out free coloring pages from the Internet like the ones here: https://www.crayola.com/free-coloring-pages/adult-coloring-pages/)
Color by number
Crochet or knitting (lots of good online tutorials and making a scarf is a good first project)
Modeling clay (just reuse the same clay over and over again if you want to save money/supplies)
Yoga
Walking on a treadmill or riding an exercise bike
Weightlifting with free weights at home
Tai chi
Best of luck, I know this type of thing is tough. Try to stick to regular wake/sleep cycles as much as possible and get outside during the day if you can, it definitely helps. Sending hugs and hoping things get better soon.