To close down (or archive) internal Slack channels, follow these steps:
For desktop:
- Click on the channel name to open the channel.
- Click the three dots (More actions) in the top right corner of the channel details.
- Select "Archive channel". Confirm the action when prompted.
For mobile:
- Tap on the channel you wish to archive.
- Tap the channel name at the top of the screen.
- Tap on the gear icon or "More actions" (three dots).
- Archive Channel: Select "Archive channel" and confirm.
Only workspace admins or the channel creator can archive a channel.
Archiving a channel makes it inactive, but the message history will still be accessible for future reference.
PS: if you're using Slack, you might be interested in Campsite.