Do note that if you used a published_at field in some of your models or did follow the Scheduled publication guide and used a published_at field, you do need to migrate.
Use the ‘Migration guide from 3.1.x to 3.2.x’ migration guide:
https://strapi.io/documentation/v3.x/migration-guide/migration-guide-3.1.x-to-3.2.x.html