>>96381999
You can do fantasy in a modern setting. Shadowrun does it, among others. The thing is, if any fantasy element is and has been an overt, well-known thing, the world is going to be unrecognizable. So if you wanna have a setting that is close to Real Earth and Real Earth History, having the fantastic stuff be secret is necessary.

I do it the historic way. The supernatural has always been a part of our world, but took different forms at different times. After the Flood, most of the monsters and giants were killed, and so they became things of myth. After Babel, the supernatural became splintered into a hundred different lores, and different entities attached to different areas or peoples. After the Incarnation, the surviving monsters and spirits were forced to go further into seclusion as they couldn't bear the proximity of the Church, and many so-called gods and sorcerers found their powers were not as effective on Christians as they had been on heathens, so they were forced likewise to practice their arts in secret. Only in the modern era, as the influence of the Church dwindles and people apostatize, have the old powers begun to resurface. But, fearful of triggering a reaction from their enemy, they inculcate themselves among humanity under the guise of rationality. AI, psychotropics, mass media, shady international oligarchic networks, all of these things they employ to keep the true nature of their existence hidden so that they can have their cake and eat it too. As the eponymous demon says in C.S. Lewis's Screwtape Letters,
>I have great hopes that we shall learn in due time how to emotionalise and mythologise their science to such an extent that what is, in effect, belief in us, (though not under that name) will creep in while the human mind remains closed to belief in the Enemy. The “Life Force”, the worship of sex, and some aspects of Psychoanalysis, may here prove useful. If once we can produce our perfect work — the Materialist Magician."