Slack is now giving itself the right to use customer data to train AI systems capable of autocompleting user input, conditioned on a manual email opt out from the workspace owner rather than using the actual settings page.

https://slack.com/intl/es-la/trust/data-management/privacy-principles

This is possibly an extremely clumsy way to sell an innocent new feature, but more likely it's an attempt to slurp up all you ever written on slack and feed it into an LLM model in exchange for money from Microsoft or Google.