The issue is less the wear and tear of the battery and motors and more the wear and tear of everything else -- suspension and brake components are going to need replacing, along with radar and ultrasonic modules, etc. These parts will be at least partially end-of-life and hard to get by the end of that 20 year period. Federal law requires some amount of parts availability for 10 years + some release of part designs to the aftermarket after that, but I have a hard time getting parts for 21 year old Ford designs that were less than popular, so I would be surprised if early Tesla models are having an easy time 20 years on. This gets much much worse as you start to look at the number of abandoned EV models from the Big 3, the abandoned/dead/dying companies (Fiskar, Lucid, Lordstown, etc). That doesn't hit the vast majority of all EVs, which are just Tesla, but it does put a dent/makes the buying decision harder. Now expand that to not just Tesla, but what does Tesla do with a Cybertruck? Like all things, the specific product decision matters a lot, and this is a new area (even at 14 years old) so there will be lots of people who optimized for cost and not maintainability.
The surprising thing is that parts availability is even worse for new cars. Sensors are built into every part now, so it's no longer just a windscreen or a bumper. If those sensors are critical to the driver assist systems, the car can be a write-off for trivial damage because of the difficulty of getting parts. And in many places, you can't just disable those systems and get on with things, even if the car is otherwise perfectly fine, because the law states that roadworthiness requires the original safety systems to be intact.
Even more alarmingly, the speed of revisions now is such that vehicles can have parts that were only used for a very short run before being updated and replaced. Your particular vehicle batch may not necessarily have identical parts to other batches even within the same generation. We're a long, long way from the way things used to be, when parts commonality stretched for decades.