Docker service is still running under OS after removing Docker extension via Plesk UI:
# systemctl status docker.service | grep Active
Active: active (running) since Sat 2022-01-25 17:32:45 UTC; 4min 4s ago
Expected behavior because Docker service can be used independently from Plesk.
Deletion of the Plesk Docker extension removes only integration between Plesk and Docker service.
In case it is required to remove the Docker service completely, apply one of the solutions below:
Note: Server reboot is required to remove Docker completely. Also user data and sites can be affected by the full removal of Docker.