Unfortunately, we can't remove/hide any options from 'Activity Type' list, which is by-deisgn.
Maybe you can create a new idea through the below URL, then ask your colleagues to raise up the votes. Ideas (dynamics.com) Our product team has direct visibility of these ideas and they will implement it on the basis of the highest number of votes received.
I hope you can mark my answerverifiedif it is helpful! If you have any questions, please feel free to contact me.
Regards,
Leah
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