You must be a System Admin, Team Admin, or Channel Admin to convert public channels to private channels.
Default channels such as
Town Square and
Off-Topic can’t be converted to private channels.
To convert a public channel to a private channel, select the public channel name at the top of the center pane to access the drop-down menu, then select Convert to Private Channel.
When a channel is converted from public to private, its history and membership are preserved. Membership in a private channel remains as invitation only. Publicly-shared files remain accessible to anyone with the link.
Due to potential security concerns with sharing private channel history, only System Admins can convert private channels to public channels via System Console > Channels > Edit (Channel Configuration).
Alternatively, System Admins can perform this action using the mmctl channel modify command.