(... 'sin city effect' usually discribes that b/w-plus-one-color effect, e.g. red lips...) 😉
To create this graphic novel look, iMovie hasn't many to offer, the picture-adjustments are limited to desaturate = making it b/w, and apply extreme contrasts:

So, what you should do is:
on recording the video, avoid shallow-focus (wrong in my example, Sin City has no blurrs at all), create hard contrasts by using lots of light, create lots of shadow... get familiar with your camera to set the aperture/speed manually
plus, camera angles, 'weird' perspectives etc etc...
get inspired by the original 😉