In channels, you can only @-mention individuals or the channel name. I believe @Everyone is only available in chats. You'll have to use channels. Channels enab

In channels, you can only @-mention individuals or the channel name. I believe @Everyone is only available in chats. You'll have to use channels. Channels enable connectors like webhooks*, and it's the only way to speak to folks outside being invited to chats. * Webhooks will be deprecated in a few months in favor of Power Automate.