The Vedanta is a difficult subject. Very difficult subject. That there is nothing at all outside, and it is only the mind moving outside as is proclaimed by the Vijnanvada theory of Buddhism, is refuted. Acharya Sankara's commentary is elaborate, worth reading again and again. A non-existent idea, an impossible idea cannot arise in the mind.
Every idea has some meaning.
Nonsensical ideas cannot arise in the mind. Even if you agree that there is some appearance outside, and really things do not exist, the appearance has to be outside. This outsideness must be accepted first. There is an outright condemnation and criticism of Vijnavada that you cannot go on saying that there is an appearance of something being outside unless there is really something outside. A rope appears as a snake but even for that appearance, the rope must be existing.