It could very well be that I am misunderstanding how MQTT normally is used with Home Assistant, thus asking the wrong questions.
The application I am looking into at the moment is for monitoring the status of a Windows PC, and especially whether the attached display is in standby or not.
Some options could be “IOT Link” or “Win 10 Assistant”, which work through MQTT.
I did not use MQTT at all up to now (I even didn’t install it yet), so that’s why I am looking into MQTT now. And while reading about MQTT and trying to understand it (in general, so not specifically for those applications), I understood that wildcards are used to make selections in the MQTT tree, and I assumed that Home Assistant would work like that as well. But this is not the case at all?
Is it not an option to use the MQTT wildcard filtering in HA Automations to access specific entities?