docs/developer/upgrades/3.5-to-3.6.mdx
Spree 3.6 requires Rails 5.2 at a minimum. Please follow the official Rails guide to upgrade your application.
bundle update
Please follow the official paperclip guide if you want to use ActiveStorage instead of paperclip.
You can still use paperclip for attachment management by setting SPREE_USE_PAPERCLIP environment variable to true, but keep in mind that paperclip is DEPRECATED and we will remove paperclip support in Spree 4.0.
rake railties:install:migrations
rails db:migrate
You're good to go!
For information about changes contained within this release, please read the 3.6.0 Release Notes.