Does Istikhara prayer become void if the supplicant has a prior desire for a specific matter, and what should one do to get rid of that? Is it a condition that the vision of Istikhara be in a dream?

Among the etiquettes of Salatul-Istikhara (prayer for guidance) are disavowing one's own power, strength, and knowledge, and instead relying on Allah and entrusting the matter to Him, accustoming oneself to be content with whatever Allah chooses. If a servant is sincere in this, Allah will choose for him what is good and expand his breast for it. He must then rely on Allah and proceed with what his heart is inclined towards. The one seeking guidance should completely abandon his own choice, because Istikhara is for Allah, not for personal desire. As for the manifestation of the effect of Istikhara in a dream, this is not correct. What Allah Almighty destines is the good, and that is the effect of Istikhara. The sign of accepted Istikhara is the expansion of the breast, not dreams.