I have used Drupal version 9.1.9, cloned the 8.1.x version of this module and...

I have used Drupal version 9.1.9, cloned the 8.1.x version of this module and installed, enabled it.

After click on run rector, I got an issue "Rector executable not found. This would happen if the composer dependencies were not installed. Did you use composer to install the module?"

I installed the module dependencies using composer, cleared the cache, still the same issue.