Virtual Texture is not available as an option for the Material Domain. Even if Virtual Texture support is enabled in the project settings.
Tested in //UE4/Release-4.25 @ CL 14469661 and this did NOT occur, so marking as a Regression.
Virtual Texture is not listed as one of the Material Domain options
The option to set Virtual Texture as the Material Domain would be available
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-113395 in the post.