Hi @Bfreak
Welcome to the HiveMQ Community! I agree with you regarding the lack of documentation of these modules but you are looking into the wrong documentation, the one you have shared just has some basic AT commands, please take a look into this one that provides AT MQTT TLS commands samples.
There is a thread where another forum member was able to connect a SIM7600 device. It might be useful to use it as a reference for the SIMCOM7080G module.
The root certificate needed to connect to HiveMQ Cloud can be downloaded from https://letsencrypt.org/certs/isrgrootx1.pem . This will create a file isrgrootx1.pem which should be used as a “server certificate”.
Another suggestion is to always use the latest firmware version available to avoid any issue related to MQTT compatibility on older firmware versions.
Kind regards,
Diego from HiveMQ Team