How can I disable logging of specific library?

Good idea, but no, I see ExMQTT logs:
they are all prefixed with [ExMQTT]

[debug] [ExMQTT] Connecting to localhost:1883
....
[debug] [ExMQTT] Connected #PID<0.711.0>

Another thing to be aware is that you need recompile the deps after setting up the config.

Yeah, I’ve tried it:

rm -rf _build
rm -rf deps
mix deps.get
mix deps.compile
mix phx.server

I’m starting to think maybe there is something specific to running the app with mix phx.server that is breaking this for me

UPD:
I fixed it with this:

# Do not include metadata nor timestamps in development logs
config :logger, :console, format: "[$level] $message\n"

Logger.put_module_level(ExMQTT, :error)
Logger.put_module_level(:emqtt, :error)

I don’t really like that those put_module_level are not part of config :logger section, but I was not able to figure out how to do it otherwise (and compile_time_purge_matching also did not work, not sure why - don’t really care in this case)