I haven't had a chance to look at this in any detail but it sounds good.
gBridge is an application, that provides a Bridge between Google Assistant smart home devices and MQTT, an open and available messaging protocol that is supported by many smart home applications and devices.
mic "Hey Google, set the ceiling light to 43%." arrow_forward gBridge/u1/ceiling_light/brightness: 43
Since gBridge is an open source project, you can host it on your own systems.
There is both a hosted and self hosted version.