The public channel you mentioned means "https://steem.chat/channel/witness", but I think there are other special channels. Because some of the witnesses had already been updated to version 20.10 before the updates were released and mentioned on the channel.
As you mentioned, you need a public channel for quick sharing. Is there a condition for accessing channels for special members?
For high risk scenarios like this a private channel for the top 20 witnesses, plus those witnesses close to the top 20, is required for security reasons. Such a channel exists and the only requirement for entry is one's position in the witness rankings. If a witness is in the top 20 they are in that slack. If there is a chance they may enter the top 20 (e.g. if they are close) they should be in that slack and if they are not, they should contact me at [email protected].
It's a long way to top, but thank you for the information. I'll contact you if it gets closer.