I was wondering if there is a possibility to un-invite people, once they have been invited in a PM thread or if I need to create a totally new PM thread.
This is two topics not one, can you split your other topic into a new meta topic please.
You can turn off notifications for a topic by entering it and setting the notification drop down control to “regular” at the bottom.
There will be a way to do this from the topic list and on multiple topics rather than entering each individual topic soon.
Staff can click the (x) next to the user’s name to remove them from the PM list, but I just checked on try.discourse.org and regular users don’t seem to be be able to do this. (actually is this a regression @sam? I remember being able to remove people from PMs at some point when we accidentally added that one guy to a PM and we were like uhhh ooops)
Anyway, if you want to suppress the PM topic, use the notification control at the bottom and set it to muted.