Most activist groups will leave flyers in your local coffee shops and libraries. That and literally just googling "local activist groups" wouldn't be a bad place to start

Plenty of groups just need data entry if you can't do much outside of the house. Otherwise educating yourself and your friends and family goes a long way. Try to keep in touch with your neighbors. Support where you can as you can

They're often networked pretty well so check in with the bigger orgs, Food Not Bombs, or Mutual Aid Disaster Relief asking then to point you towards local orgs.

You may also be able to find an org by searching. "Mutual aid" + your nearest city, state, or alternative name for region (e.g. "twin cities").

Blue sky might be a good resource.