Unfortunately, as far as I know, mentioning everyone (or anyone) through a
@channel is not possible through the public Slack API. At least the last time we checked that was the case - if you can find any docs how this could be enabled we’d be of course happy to add the option to the Step.
What we usually do is that we have a separate channel for these notifications, and we enable all relevant notifications for ourselves for that channel. Internal rule is to keep general chatting outside of these channels, only alert/relevant chats are allowed.
We have more than one of these channels aggregated from various sources, and each team member joins the relevant channel(s).
I hope this helps, and if you have any questions just let us know!