One common option I've seen in companies I've worked in was to have multiple Slack Channels, one for work, one for general chat.
You can then enforce a strict nohello policy on the work channel on the understanding that the general-chat channel may not receive priority response.

This can be explained in the header for the channel as a rule, and therefore not be considered rudeness.

You can enforce it with a slackbot scanning for keywords and short messages as other Answers here have suggested.

One common option I've seen in companies I've worked in was to have multiple Slack channels, one for work and one for general chat. You can then enforce a strict nohello policy on the work channel on the understanding that the general-chat channel may not receive priority response.

This can be explained in the header for the channel as a rule, and therefore not be considered rudeness.

You can enforce it with a Slack bot scanning for keywords and short messages as other answers here have suggested.