Wire a bathroom fan and light so the light always controls the fan, but the fan can be operated independantly from the light
You could do that with a double pole switch and a single pole normal switch.  Wire the hot to both of the line side poles on the double pole switch as well as to the single pole switch.
Wire both the fan and the light to individual poles on switched side of the double pole switch.  Then run a jumper from the pole that controls the fan on the double pole switch to the switched side of the single pole switch.  All the neutrals and grounds stay connected as they are. Don't get confused with a 3-way or 4-way switch, those are different animals.  You may have to go to an electrical supply house to get a true double pole wall switch.
I could provide a diagram if you want.   But I want to post this quickly to beat out the big 3!  LOL  Competition for points here is fierce!  LOL

Carl asked me to provide more info.  This what I have time for right now. If others wanted to contribute a better diagram, that's welcome.