I noticed this warning in the Home Assistant docs:
I’ve been using Mosquitto for years with no complaints and no issues. And I’ve used some very complicated setups.
Using another server as the broker is definitely an option. But you will have to customize the config so both openHAB and the UI point to that external broker instead of the internal one. The internal one is required because the HestiaPi has to be self contained.
And again, of course you can configure openHAB to pub/sub to another broker for temp changes (see Integration with ANAVI Thermometer) an I’ve already provided the tutorial for how to command it from an external program. The main complaint, as I can see it, is that the configuration is complicated. Unfortunately I don’t know of any way to make it simpler. But it’s all possible.