Additional features, settings, or issues not covered by specific Microsoft Teams categories
Hello Torsus,
According to my knowledge, it is not feasible to make some team members invisible for other members. Regarding to the hidden channels you mentioned, Teams automatically shows the five most popular channels in every new team you join. The rest of the channels are still available to all the team members.
As per your requirement, I think you may try Private channels. Private channels create focused spaces for collaboration within your teams. Only the private channel members can see and access the channels. For more details, you can refer to this article: Private channels in Microsoft Teams
Hope the information above helps!
Regards,
Rick