Are you testing this with a digital multimeter or an analog multimeter? you shouldn’t be getting a different voltage when you reverse the leads if the meter is in AC mode.
And if you are still seeing this
Voltage across the Rh & C terminals with Rh at - or + and C at - or + of multimeter is 26 volts
Then I’ve got no idea of what wyze has done with their internal design of the thermostat. This should not be possible if Rh is properly isolated. If I wasn’t using my thermostat to heat my house, I would test it on my system with my fluke meter, because this shouldn’t be possible. If there is indeed 24VAC across Rh and C, then you will have to use an isolation relay.