It is often said that Satan has 'already lost' the war with God; and this is certainly true in one sense, but not in another.
The sense in which Satan has already lost is that since Jesus Christ established Heaven and opened it to anyone who genuinely wants to go there after death; there is an eternal realm where Satan has no influence.
So - after death and eternally, Satan has lost.
But Satan keeps fighting the spiritual war because there are billions of individual souls who may choose to reject the gift of resurrection to eternal life; and in the billions of individual battles of that war of salvation - the outcome remains undecided.
For those souls who have rejected Heaven - there are presumably short-term satisfactions (spiteful pleasures) to be attained in the work of tormenting and damning other souls in the realms outside of Heaven, including this earth. And it seems quite likely that - on this temporary earth and among mortals subject to entropy - the Satanic powers are winning (or have won) the spiritual war, overall.
But, again, in the other direction; these gratifications are temporary; because at some point the mortal life on earth 'school' will come to an end; and then the damned souls will face a bleak prospect of inevitable decline towards some kind of solitary state of resentful misery, eternally.
Therefore, Satan has probably won the war for earth, overall; but the battles continue for the fate of each individual soul; while in Heaven, Satan has already been defeated finally and forever.
It is the complexity of this situation - with different answers from preferences for different timescales, and priorities relating to different locations - which is why some people have chosen (and still choose, in apparently increasing numbers) to ally with Satan.