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.