This is mostly about light control, not expensive gear.

The key is to keep the room very dark and allow only a narrow beam of light to hit the subject. A simple way is to place the subject in a dark room facing a slightly opened door or a window with the blinds nearly closed. That creates the slit of light naturally. If needed, you can place your flash outside the doorway/window area to boost that beam.

Using flash inside the room is harder because it tends to bounce and fill the whole space, lighting the background and face more than you want. To reduce that, cut ambient exposure with low ISO, a smaller aperture, and a faster shutter speed, then add only the controlled light.

To localize the light, use flags or black foam board to block spill and leave only a small opening for the light. For a softer look, diffuse the light or bounce it off a white surface. Even simple DIY modifiers can work.

So yes: setup is the main issue. Extra modifiers can help, but careful blocking, darkness, and a narrow light source matter most.