where are the demons now that were here during the ministry of Jesus?
They are eternal beings. Their geographic locality is not something we can fathom because they inhabit the unseen spiritual realm, where time and physicality do not matter... all that DOES matter in their world is Holiness and Transgression.
This is the Bible emphasizes how, after the Cross, we have in our power to overcome them through submitting to God; in other words, resisting Satan’s temptation to sin through the power of the Holy Spirit.
In a roundabout way to answer the questions raised on this thread...
... the true portrait of “spiritual warfare” or how we are to deal with the Enemy is what Jesus did in the forty days temptation in the desert.