Making private Matrix room public

is it possible to make a invite only room → public?

Yes it is.
Right click on the channel to which you want to create an invite and go to “Create Invite”

I just realized you are talking about the chat :man_facepalming:
Currently you can only invite existing friends, you can’t create an invite link yet.

Thx, but I mean a room, in the Teamspeak client chat system. Which is set to “invite only” however I would like to change this to public so that anyone can join and does not need a link.

If you have already created a private room, there is no option to switch it to public, but you can create a new room where you have the option to choose “Public”.

This should be suggested in the next update to include this option so that you can switch the private room to public.

You must create a public room then. There is no way without hacky things in our database to change it.