So, the reality is, getting out on any bike e or no is better than not riding a bike. There are proven health benefits for ebikes too, it's not as much as non ebike, but it's also non negligible.
IMO yes, start with a non ebike, but for a 20 mile commute, get an ebike. You're already going to need to find another route, so it isn't going to be a straight 20 miles, and if you're doing it every day, the days you're late you're gonna drive, whereas with an Ebike, you're more likely to do it every day. So set yourself up for success and get a cheap gravel bike and then a commuter centric ebike. Now to be clear, not the ebikes you don't have to pedal. Get a tern hsd or something.
I am an avid cyclist, and I love having an ebike in the stable so that on days I'm late, I can still stay on a bike vs driving. Just stay away from the "ebikes" that you don't pedal. Look for ones with the motor inbetween the pedals. I also kind of think saying to stay away from an ebike because you're trying to get in shape is backwards. An ebike is an easier stepping stone towards being more active assuming you get the right kind.
Consistency is typically better for getting in shape than how hard you do it. So if you bike 1 or 2 times a week because you're biking on the weekends, vs 5 (10 since 2x a day) commuting to work, the commuting on an ebike is probably going to actually net you more than the weekend warrior exercise.
Edit: one more thing. Route route route. It's been said above, but finding the most bike friendly route to get somewhere is absolutely key. That means not biking on 55mph roads.