My 2021 Mazda CX-30 is having gear change issues on inclines

This behaviour is probably a function of the way Mazda has calibrated the cruise control. In order for the car to initiate a downshift to regain some lost speed on a hill, it needs to recognise that it has, in fact, slowed down. But if it shifted down after losing just a single kilometre per hour, you’d find it would be constantly shifting gears in even slightly hilly terrain. And that would probably be even more annoying. The fact that it then overruns the set speed is probably the tall gearing (and physics) letting the car momentarily push through your 111km/h setting before it settles back to that speed.

But it’s worth keeping an eye on the speedometer even when using cruise-control, as this behaviour won’t work as an excuse during any roadside chats with the Highway Patrol.