It's written in C. At this point, this is an instant disqualification for a network service.

I looked at MQTT options earlier last year, and the best one was Mochi ( https://github.com/mochi-mqtt/server ), written in Go.

I added TLS support with Let's Encrypt provisioning to it: https://github.com/Cyberax/lenc-mochi

Oh boy. You're going to hate to know what programming language is used for apache, nginx, postfix, postgres, MySQL/mariadb, redis, wireguard and the majority of network hardware.