I regard evil as having been a part of primary reality. Evil is the rejection of Good; and Good is God's creation.
God has to cope-with, work-with pre-existent evil.
Some Beings are intrinsically (from eternity) incapable of love (these are the demons).
These will always and forever reject God/ Good/ Creation because that is the world of love, built with love - it is love that makes Creation coherent, harmonious. So, demons cannot be saved; they lack that which would make salvation possible (i.e. the capacity for love).
God has to work with these evil beings, incapable of love - because they are immortal and indestructible spirits.
But God's main aims and interests are those Beings who are capable of love; and God's hope is that as many as possible of these will choose Heaven.
In mortal life - which is a finite, temporary, always-changing state of incarnation; 'designed' for experiencing and learning - evil is included. Human Beings capable of love will, during mortal life, therefore experience both Good and evil (tatstes of Heaven and hell) - and after mortal life will be offered the gift of immortal resurrected life in Heaven; which is a permanent choice.
This choice can be made on the experiences of mortal life, which are (normally, usually) tailored by God such that we will have sufficient of the right kind of experience that each specific Human Being can make this choice, can decide in favour of resurrection - which involves loving/ trusting/ having-faith in Jesus, and following through the transformation that is resurrection.
Thus evil is made-use-of by God during mortal life. Mortal life takes the form of a contest (a spiritual war) focused on those Human Beings (and perhaps other beings) that are capable of love - in relation to the choice for or against Heaven that each will make after biological death.