[Periodic reminder — this channel is meant for announcements about this Slack/Community, posted by admins. If you'd like to announce something to the group at large, please do it in #C5U3SEW6A, #C01932BJGE8, or #C5T9GPWFL. When in doubt, consult the Member Handbook at https://futureofcoding.org/member-handbook. Thanks!]

I could have sworn there was a way to make channels postable only by admins?

You can set the one default #general channel to be admin-only. But we've been using that channel as the main hub for on-topic discussions (it's now #C5T9GPWFL), so there's no way to turn that into the admin-only announcements channel without weirdly breaking continuity and our history search tools.

I'm definitely in Slacks where there is a read-only announcements channel that only allows for admin posting and a general channel as well

It could also be where they rename #general to #CGMJ7323Z (or whatever), and then make a new #general. We could have done that, but it would have broken continuity — that's the reason we didn't do it.