Install
https://www.howtoforge.de/anleitung/so-installierst-du-mosquitto-mqtt-server-unter-ubuntu-22-04/

sudo apt-get install -y curl gnupg2 wget git apt-transport-https ca-certificates software-properties-common
sudo add-apt-repository -y ppa:mosquitto-dev/mosquitto-ppa
sudo apt install mosquitto mosquitto-clients -y

sudo mosquitto_passwd -c -b /etc/mosquitto/passwd foo pass1234

# todo sudo
cat < /etc/mosquitto/conf.d/default.conf
listener 1883
password_file /etc/mosquitto/passwd
EOF
chmod a+r /etc/mosquitto/passwd

sudo systemctl restart mosquitto

Debug MQTT
http://mqtt-explorer.com/
https://snapcraft.io/install/mqtt-explorer/ubuntu#install

sudo snap install mqtt-explorer