Front porch light has low voltage

Went to Replace a burned out light bulb. The new bulb didn’t work either. Replaced the double switch, one side of the switch works. The switch for the porch light doesn’t, it has 0.9 volts. In the switch box I m seeing all of the common wires put together with a wire nut. All the hot wires are hooked up on the switch. I’m guessing all the switch is used for is an interrupter switch for the black wiring. I don’t know it blows my mind.