Hi @Rhodes, Lindsay
At the moment, we don't have the option to switch channel mode. The only way to have a private channel is to create it from the beginning.
To get this feature more quickly, I have found a feedback in Teams UserVoice and you could vote for it. Many features of our current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future. Thanks for your understanding and support.
Feedback: https://feedbackportal.microsoft.com/feedback/idea/c33e3449-9e79-ec11-a81b-0022484f5e0c
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