yeah.. it takes some googling, but a few devices (eg. sonoff plugs) can be flashed with tasmota, and some (mostly zigbee) can be used directly with a usb dongle

yeah.. it takes some googling, but a few devices (eg. sonoff plugs) can be flashed with tasmota, and some (mostly zigbee) can be used directly with a usb dongle and zigbee2mqtt, without any vendor-based cloud service (eg. tuya valves for radiators, ikea bulbs, sensors,...). But yeah, either way, you have to do research before you buy the device :)