When you say 1 switch do you mean 1 switch or 1 switch plate with 2 switches and 1 dimmer? Have you got cabling in to all 3 circuits back to the switch position?
As above if your happy to not dim the dimmable leds then you can. If you do want to dim the dimmable leds you will need a click mode 2 gang switch and swap 1 switch for a click mode led dimmer module.
If all you want to do is turn on all 3 items with the 1 switch, then as above, a standard On/Off switch will do this. Of course you would not be able to dim the dimmable LEDs. They would just be on or off.
If you want to dim the dimmable LEDs and switch the fan and non-dimmable LEDs on then you can't do this with a standard dimmer switch or On/Off switch.
You may be able to use a dimmer switch and add additional equipment (like this) to the fan and non-dimmable LEDs circuits that could detect the sign wave of the dimmer and then switch on fully. I'd have to test this to see if it works correctly though. The relay may not like a chopped sign wave. This would also involve extra wiring.
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