It is currently not possible to delete all activity feeds. To get this feature more quickly, I have found a feedback in Teams UserVoice and you could vote for it.
Feedback: https://feedbackportal.microsoft.com/feedback/idea/164521c4-7f67-ed11-a81b.
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!
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