The answer must be split into two parts, depending on whether we are dealing with a voice channel (Teamspeak’s standard) or a text channel (what I use most on Discord).
For a voice channel, you can either leave channel entirely untranslated or you can use Kanal analogously to Funkkanal. Thus, both the following are possible:
Wir treffen uns dann um halb fünf im Raid-Kanal. Push-to-Talk an machen!
Verdammt, ich finde den Channel nicht mehr, dabei will ich doch mitreden!
For a text channel, I would be hesitant to use either word. Instead, I would be inclined to interpret the text channels as a chat and thus the single channel would be a chat room. And the room can also be translated:
In welchem Chat kann ich dumme Witze reißen?
Dafür haben wir einen extra Ignorier-mich-Chatraum.
Und in das Chatroom kommt jeder rein?
Ja, aber nicht mehr raus.
I will acknowledge, however, that Discord’s official German help page uses the term Kanal for text channels, which had me looking twice whether they really meant text.