I don't see a release under Downloads on the Drupal Project page: https://www.drupal.org/project/webform_civicrm
1 Answer
Two options:
1) look for and download the 8.x-5.x-dev version [this is updated every couple of months/I will try make that weeks]:
https://www.drupal.org/project/webform_civicrm/releases/8.x-5.x-dev
2) or check out the 8.x-5.x branch from the GitHub repo to always be on the latest:
git clone https://github.com/colemanw/webform_civicrm.git --branch 8.x-5.x
and then:
git pull