Solved!
I was using a GPIO controller, but the PWM doesn't work with the default mapping configuration of Recalbox. The solution is to set controllers.gpio.args=map=1 in the recalbox.conf file.
Now the GPIO and the PWM Audio are working simultaneously.
My PWM config is:
dtoverlay=pwm,pin=13,func=4
@svartholm I changed my mind, I think the audio problem is present if you set the gpio and the pwm-2chan enabled at the same time. Everything was working until I decided to enable the gpio in the recalbox.conf file. Now I don't have sound 
@svartholm Hi guys!
yes, it's fixed, but I'm not sure about what's the solution. I think there's something broken in the 4.0.2 update. I read other thread in this forum about a similar problem with RPi3 and Recalbox 4.0.2. I decided to downgrade to the 4.0.0 version and disable the automatic updates and everything is working now!
Let me know if it works for you!
Hi guys!
I'm completely crazy! I have been trying to fix the sound output for hours! I'm building a GameBoy Zero. I enabled the GPIO controller and tried to activate the PWM audio output.
My GPIO18 is used by the Y button of the controller, so I changed the dtoverlay line to use the GPIO13.
This is my current configuration:
I'm using earphones directly connected to the GND and GPIO13, but nothing sounds. I tried different combinations of pwm and pwm-2chan without results.
My Recalbox version is 4.0.2
Could you please give me some advice? Thanks!!!! 