Current problem
Currently, if you mute a channel it retains its unreads. This has the undesirable side effect that if you enable the setting in that community to hide muted channels, the now-muted channel that still has unreads is still visible because of the unreads.
Proposed change
I propose that when you mute a channel (and maybe even category?) it should also mark that channel as read. Muting a channel is a pretty intentional action by the user, and forcing them to take that extra action to mark as read just to be able to hide the channel is a bit unintuitive and feels unnecessary.
Platform
macOS, Windows, Linux, Web, Android, iOS