See here: https://www.reddit.com/r/GalaxyNote9/comments/9j9j8l/otterbox_defender_vs_defender_pro_alpha_glass/

Some online reviewers who reviewed the iPhone version say that the Defender Pro is slightly thicker, but that might be because the regular defender for iPhones leaves a big hole in the middle to show off the Apple logo. And then there's the person in the link above who wrote this:

I also was curious so I called. They told me the only difference is the microbial protection from "dirty work germs". The warranty , drop protection etc is all the same.

The Pro version also seems to have lines etched into the back. I don't know if this helps get better grip or something, or if it's just for decoration.

I have the regular defender for the S10 if you have any questions about it. It's a little thinner than the older defenders I've used, the ones which had built-in screen protectors. It's a nice case though, and I love the color on the blue one.