Crackdown 3's Gamescom tech demo details how its destructible environments work.
Initially we see that you can shoot holes through walls, which crumble a little more with each shot. What's interesting is that if you create a circle of holes the middle piece will just fall out. In short: you can chisel out your own doors.
You can also shoot down bridges and watch buildings crumble in real time. It's a bit like Earth Defense Force 2017's wonton destruction only with actual physics.
It's worth noting that this isn't entirely representative of how the game will actually play. The weapons in this tech demo are overpowered to show off the game's destruction. It probably won't be possible to raze a city quite to effortlessly in the final game, but it should hopefully play fairly similar to what we see here.