The Apple Watch Pro will get an additional button on the left side, according to an image of the case posted by blogger Sonia Dixon. Presumably, this button will be used in fitness applications.
On the left side there may be another button that is not protected in any way. But it can also be a speaker, because it has to stay open, and in the usual place it is not.
Leaked Apple Watch Pro case accessory shows two extra buttons | AppleInsider
Images of what are claimed to be Apple Watch Pro cases, include a cutout for one extra button, and what could be a protective cover for a second.
appleinsider.com