Hi @Sterneder, Simon ,
Unfortunately though it is, as per my knowledge, it is impossible to create custom permission role in a private Teams channel. I would suggest you raise a user vocie here: https://microsoftteams.uservoice.com/. It is a place for customers provide feedback about Microsoft Teams products. What's more, if a feedback is high voted there by other customers, it will be promising that Microsoft Product Team will take it into consideration when designing the next version in the future.
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