Can you pickle avocados?
I've never heard of it being done and I can't imagine why you'd want to try. An avocado is 70-80% water and 15% fat. That means you would basically be making pickled fat.

Compare to cucumbers and peppers which are both in the range of 0.1 to 0.2% fat, and much firmer than even an unripe avocado when raw.

I'm sure that it would be safe as long as it's done properly and the pH is under 4.6, and the acidity would kill or slow down the enzymes enough to prevent it from turning black. But I don't think it would be edible, even if you added oil to the mix. We are biologically hardwired to perceive sour fat as being rancid, and unlike certain pickled meats, there's no umami in there to compete with that sensation.

If you feel you must try this, at least start with an unripe avocado and see what it's like after a few days. A ripe avocado would almost certainly disintegrate in a pickling brine.