Are smart doorbell chimes brand-locked?

Mostly, yes. Ring chimes only pair with Ring devices, eufy's add-on chime only works with specific eufy doorbells (E340/C30/C31), the myQ Chime only pairs with myQ hardware, and Arlo Chime 2 only works with select Arlo cameras and doorbells (not Pro or Ultra, per the product listing). If you want a universal solution, a wired traditional chime like the Newhouse CHM3D is the more flexible route, provided your doorbell supports a mechanical chime.