Did you restart PMS after deleting the driver?
I’m running 1.18.4.2171 on a DS918+ and transcoding works with the driver deleted.
Maybe try the following:
- Via the Package Center, stop and remove PMS.
- Download the latest version from https://www.plex.tv/media-server-downloads/#plex-media-server.
- Install, but do not start, latest version via Package Center.
- Delete the offending driver (instructions).
- Via the Package Center, start PMS.