Bluetooth can do it locally, but yes, for things on ZigBee or Z-Wave, it’s gotta have an antenna hub. WiFi switches and lights most likely do “phone-home” to the cloud in some way (usually for color or brightness control via app, Govee especially loves this). The down side, other than the obvious privacy implications, is that if your ISP has an outage, so do your switches.

Home Assistant attempts to mitigate both the privacy and offline issues, while putting all of the different brands and hubs into one place.