A hybrid work policy is the written rulebook for how office and remote days work: how many days, which days, who decides, and what happens when the office is full. Good policies also cover equipment, expenses and how performance is assessed across locations.
The policies that stick are the ones the tooling can enforce gently. If the policy says three days in, the schedule app should make those days easy to plan and the office easy to book, rather than leaving compliance to spreadsheet policing.