I think that’s a little harsh - openHAB has a dedicated MQTT binding used by many, and I’m sure if there was one of these databases in existence it’d be useful knowledge that one of us might know.
But I think the answer’s already been given. Consumer devices don’t tend to ship with MQTT, so a database doesn’t exist. The list for Tasmota devices is pretty useful if you fancy flashing a consumer device, and I guess I’d add the list of zigbee2mqtt compatible devices as the Zigbee protocol was mentioned (with zigbee2mqtt you flash the USB zigbee dongle, not the devices).