Electrical – How to connect a single pole light switch with three 2-wire cables in box

First thing you'll have to do is determine where the wire from the switch is going. I'm guessing that all those lights,fan, and receptacle are just daisy-chained with the switch interrupting the neutral inside a fixture box or separate junction box. (Why, why, why?) If you make the existing switch control only the ceiling fan, you'll of course, need to decide where you want to add a switch or switches to control the others. Additional wiring may involve crawling in the attic if there is one, drilling top plates, and dropping wire to new switch locations. That's the best I can offer given the vagueness of the problem as described. I will add that, if necessary, you could probably rent a toner and probe to trace wiring (with circuit breaker turned off). Or, more practical, find the suspected other end of the switch wire, disconnect it, and gently wire nut the pair together and then check with a multimeter for continuity at the other end to confirm that's your wire. HTH

Based on what you've shown, you should be able to wire it up like this...

However, those red Wing-Nut® twist-on wire connectors are only rated for a maximum of 6 #14 conductors. So you'll have to split up the neutrals in to two groups, and connect the groups with a pigtail between them.