Yes, a license is required for each subdomain, unless that subdomain is one of a few Elementor-recognized staging subdomains.

Subdomains that are not considered as a license use:

• dev.* (dev.example.com)
• local.* (local.example.com)
• test.* (test.example.com)
• staging.* (staging.example.com)

 See more information about using local and staging sites here.