Answer and explanation:
An ".action" file is a file written in Xcode and used by the Automator program, whose function is to create automations in macOS. Action files contains specific actions that can be combined with other actions to create an automated process.
This type of file is used to automate tasks in macOS, usually with Finder (file manager) or another program.
Action files are especially useful for repetitive tasks, such as creating sequential batch folders, editing images, or deleting files.