4-20mA output from Arduino Nano
I believe you are looking for this design

To test different levels you can change the current output by double clicking the square wave on the left and changing the duty cycle.

"analog pin" on Arduino refer to analog inputs not outputs. what you want is a DAC which outputs a voltage level. because Arduino don't have this you can use PWM and an RC filter, as shown in the above circuit

Arduino only output 5v or ground, the 3.3v output is a power supply and the level is not controllable

please make sure you are using a PWM pin seen here and not just an ADC analog input pin