There are several different ways of blocking the issue workflow transition:

Block transition if any item from the checklist is not completed (built-in validator).
Block transition if the mandatory item is not completed (built-in validator)
Block transition if the checklist is empty (build-in validator).
Block transition using regular expression (custom validator; allows to make particular items optional or check if there are any items).

Also, there is a way to complete all items automatically when the issue gets resolved (or transitioned):

Complete all items automatically when the issue is transitioned (e.g. resolved)

In Jira, the transition between workflow statuses goes through a validation phase that determines if the transition is allowed or not. The validation phase can be configured by Jira administrators through "validators". Learn more about Configuring Workflows and Workflow Validators in the Atlassian Documentation.

Block issue transition if checklist is not completed