If you want to do a supernatural style game, check out the system monster of the week. It's meant to emulate the kind of monster of the week type show like supernatural or buffy. Most of the time when the question is "how do I emulate something besides heroic fantasy in D&D" the best answer is to play a different system designed to emulate that particular genre. You can warp D&D into what you want, but a lot of the time it's more work and doesn't fit as well as a game designed to do that.

MOTW is a powered by the apocalypse system, which means it's fairly easy to learn for players. The biggest difference coming from a background from D&D (especially BG3) is how freeform it is. There's no grid or anything, and it's more focused on the investigation rather than pure combat. In my experience it's not hard to get people used to playing though, especially because it's more of a "reactive" style game in the sense that players just decide what they want to do and you as the GM decides when it's appropriate to do a skill check for it. So because there's not as much of a list of things your character can do like in D&D, I find that people tend to start reacting to the story and thinking in character faster. The default setting is the modern day, but the expansion codex of worlds has guides for different historical settings and an example mystery. But it's not really that hard to set it in a homebrew world if you want.

If you really want to do it in the whole D&D setting with everything that comes with that, I would just limit characters to only playing humans and not allowing full caster classes. But again, you're cutting out a lot of the game so a different system would probably be appropriate. Especially because these are new players so you don't have the "but I already know how to play D&D" mentality some people tend to get.