With the move of MQTT configuration from yaml to the UI is is not possible to turn off discovery at the point of configuration. You have to setup MQTT and then re-configure it to turn off discovery.
This causes a problem if you have a second HA instance that is just publishing to MQTT via MQTT statestream or @koying excellent MQTT discoverystream integration. The second HA instance configures all of the entities and devices from the homeassistant discovery topic. In my case this is 1000’s.
Can the UI MQTT configuration be updated to allow the turning off of discovery at setup