Basic etiquette would be to not force co-workers to use Slack at all. And for that matter, any other proprietary network based on closed standards that do not admit connections from third-party clients. I'm forced to use Slack and Zoom from time to time for important work stuff, and it is extremely annoying and humiliating.
This... is an insane take. It's "humiliating" for you to use the communication platform your company has chosen?
Besides, I don't work for a company, but in the public sector (which by the way I think it should not impose non-free software nor secret protocols into the citizens).