[@floodtalon]

Normally I’d refrain from revealing meta information without some rolls, but yes the cyclope is specifically immune to Hold Person because that spell only works on specifically humanoid (I.e. orcs, humans, tiefling, dragonborn) whereas Cyclopes are classified as a giant (I.e. ogres, trolls, yeti, other bipedal two armed things that aren’t classified as humanoid due to their size). You need a hold monster spell to affect a cyclope.

It’s an easy mistake, since you may argue what clearly defines a humanoid of medium size to giants of humanoid shape, but this isn’t the place for that.