Connecting your calendar keeps meetings visible inside Atwork and, more importantly, stops people booking you when you are already busy.

Prefer a different provider, or a self-hosted calendar? CalDAV connects the same way.
An amber dot means the connection needs attention — the access token expired or was revoked at Google's end. Usually a password change, a security review, or simply time.
Click Manage and reconnect. Nothing else needs redoing, and anything that depended on it resumes.
Worth checking early: while a calendar connection is broken your availability is wrong, so booking links may offer times you are not free. If someone books an occupied slot, this is the first thing to check.
Related: Connect Atwork to your tools · Set your language, calendar and timezone