Thanks to @techranger and @dean. Found room in my client. Your link @techranger pointed me to use web client I never do. So I searched for the room name and now I am successfully in. Thanks a lot.
Are there any more rooms? I remember 3 or 4 of them.
Could someone invite me to the Librem 5 channel? I left it a while ago, but would like to check in again, if someone could PM with a invite or something.