This calculated field returns the number of all issues linked to the current issue as blockers.
Create a new Calculated Number Field (by JWT) custom field and name it properly.
Providing a description will help you to identify what the custom field does but this step is optional
Add the following expression:
count(filterByResolution(linkedIssues("is blocked by"), ""))
To achieve this, the following functions are used:
Add the field to the relevant view screens.
Remember: All calculated fields are read-only and cannot be manually updated on a create or edit screen.
Once configured and added to an issue screen, the result will look like this:
Screenshot