The first step for safely sharing passwords is not doing it. SSO as much as possible, give people actual accounts where not.

As a last resource, at a Former Employer™, people put a public key in their profile, and we used GPG to encrypt secrets and paste the encrypted value on Slack/Teams. This was only among developers, and there was a tutorial for setting up the GPG GUI and encrypting values with it, so it worked fine. But we did also actively worked towards not needing that as much as possible.