I am honestly confused, A transformer "Steps up the voltage and steps down the current" or vice versa. So how does it obey Ohm's law? for example, a transformer with a winding relation of 2:3, should make 4V 30mA become 6V 20mA, right? but I=V/R, so is there some internal resistance on the secondary winding? I know that impedance could be the answer, but does varying the input resistance varies the inductance of the secondary coil?
Ohm's law describes the behavior of a resistor; it doesn't say anything about an ideal transformer.
It is true that the resistance of the windings causes a power loss and a real transformer doesn't behave like an ideal transformer.
The resistance and inductance are not directly rated, so no, changing the resistance does not necessarily change the inductance.
There is a no-load excitation current and associated conductive loss and Mutual coupling ratio from 99.9 to 90% which in smaller units can account for 10% loss and drop where they rate the output voltage at rated power. So no load can be 10% higher voltage.
There are models for this and Ohm's law may be applied with Vin(f)=I*f)*Z(f) + losses for output V,I (f).
I won't repeat them here, but they exist.