It would be a nice feature to have if admins could mute specific users per channel, making them read-only for those users.
While we do not have this feature available yet, we actually have a suggestion created in the Mattermost Uservoice platform:
However, this one is not channel specific. May I know if you are open to create a new suggestion in the https://mattermost.uservoice.com/ platform to address this? Thanks.