Files in trash show as being retained because Egnyte Secure & Govern enforces a 1-week grace period for items within the trash once any Default Retention or Retention Policy has been configured for a domain. This ensures that Secure & Govern can correctly process and keep deleted files, even if the time between file creation and deletion is very short (e.g., a user creates a file and immediately deletes it).
This grace period makes sure that Secure & Govern always enforces the retention rules you have configured, no matter what. The grace period means that deleted files cannot be purged manually, nor automatically, until one week after they have been deleted. After one week, if the deleted file is not subject to retention, it won't show "Under retention" anymore and can be purged.