Retirement does not mean you cease to contribute to society. It may allow you to develop new hobbies and passions, build or enhance relationships with family and friends, or give time to your community
Downtime may allow you to think deeply on what kind of world you want to live in, or travel may broaden your horizons and make you aware of issues you would like to address - you could become politically active, or contribute your efforts to a charity
You don't have to do any of these things, but don't write off retirement as an empty non-productive life stage. If it doesn't bring you joy, you can always go back to work ;)