Anybody in a workspace can still read and preview a public channel, and Join channel is one press. Posting, replying in a thread and starting a poll are for the people in the channel, as its member list says. An archived channel refuses changes to its name, topic and description until it is restored.
Join a public channel before you post in it
In Kemble Work, posting, replying or starting a poll in a public channel needs you to be in it, and an archived channel’s name and topic are kept as they were.