Miami has a few highly walkable pockets — South Beach, Brickell, Wynwood, the Design District, and Coconut Grove — but most of the metro is car-dependent. Metromover (free) covers downtown and Brickell; Metrorail covers a more limited north-south corridor.
South Beach, Brickell, downtown Miami, Wynwood, the Design District, and Coconut Grove are the most walkable. Each has dense retail and reasonable transit or walking distances to daily essentials.
Metromover is a free elevated people-mover covering downtown and Brickell — useful for residents of those neighborhoods. Metrorail runs roughly north-south through the western part of the city. Most other trips require driving or rideshare.
Living near where you work matters more in Miami than in most cities. Brickell and downtown for finance/tech; South Beach or Mid-Beach if you work in hospitality; Coral Gables for UM commuters.