So I've done some more ...
I've used raspi-gpio to get the status of the different gpios:
LibreELEC:~ # /flash/raspi-gpio get
BANK0 (GPIO 0 to 27):
  GPIO 00: level=1 fsel=0 alt=  func=INPUT
  GPIO 01: level=1 fsel=0 alt=  func=INPUT
  GPIO 02: level=1 fsel=0 alt=  func=INPUT
  GPIO 03: level=1 fsel=0 alt=  func=INPUT
  GPIO 04: level=1 fsel=0 alt=  func=INPUT
  GPIO 05: level=1 fsel=0 alt=  func=INPUT
  GPIO 06: level=1 fsel=0 alt=  func=INPUT
  GPIO 07: level=1 fsel=0 alt=  func=INPUT
  GPIO 08: level=1 fsel=0 alt=  func=INPUT
  GPIO 09: level=0 fsel=0 alt=  func=INPUT
  GPIO 10: level=0 fsel=0 alt=  func=INPUT
  GPIO 11: level=0 fsel=0 alt=  func=INPUT
  GPIO 12: level=0 fsel=0 alt=  func=INPUT
  GPIO 13: level=0 fsel=0 alt=  func=INPUT
  GPIO 14: level=0 fsel=0 alt=  func=INPUT
  GPIO 15: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 16: level=0 fsel=0 alt=  func=INPUT
  GPIO 17: level=1 fsel=0 alt=  func=INPUT
  GPIO 18: level=0 fsel=0 alt=  func=INPUT
  GPIO 19: level=0 fsel=0 alt=  func=INPUT
  GPIO 20: level=0 fsel=0 alt=  func=INPUT
  GPIO 21: level=0 fsel=0 alt=  func=INPUT
  GPIO 22: level=0 fsel=0 alt=  func=INPUT
  GPIO 23: level=0 fsel=0 alt=  func=INPUT
  GPIO 24: level=0 fsel=0 alt=  func=INPUT
  GPIO 25: level=0 fsel=0 alt=  func=INPUT
  GPIO 26: level=0 fsel=0 alt=  func=INPUT
  GPIO 27: level=0 fsel=0 alt=  func=INPUT
BANK1 (GPIO 28 to 45):
  GPIO 28: level=1 fsel=4 alt=0 func=SDA0
  GPIO 29: level=1 fsel=4 alt=0 func=SCL0
  GPIO 30: level=0 fsel=7 alt=3 func=CTS0
  GPIO 31: level=0 fsel=7 alt=3 func=RTS0
  GPIO 32: level=1 fsel=7 alt=3 func=TXD0
  GPIO 33: level=1 fsel=7 alt=3 func=RXD0
  GPIO 34: level=1 fsel=7 alt=3 func=SD1_CLK
  GPIO 35: level=1 fsel=7 alt=3 func=SD1_CMD
  GPIO 36: level=1 fsel=7 alt=3 func=SD1_DAT0
  GPIO 37: level=1 fsel=7 alt=3 func=SD1_DAT1
  GPIO 38: level=1 fsel=7 alt=3 func=SD1_DAT2
  GPIO 39: level=1 fsel=7 alt=3 func=SD1_DAT3
  GPIO 40: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 41: level=1 fsel=1 alt=  func=OUTPUT
  GPIO 42: level=0 fsel=0 alt=  func=INPUT
  GPIO 43: level=0 fsel=4 alt=0 func=GPCLK2
  GPIO 44: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 45: level=1 fsel=1 alt=  func=OUTPUT
BANK2 (GPIO 46 to 53):
  GPIO 46: level=1 fsel=0 alt=  func=INPUT
  GPIO 47: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 48: level=0 fsel=4 alt=0 func=SD0_CLK
  GPIO 49: level=1 fsel=4 alt=0 func=SD0_CMD
  GPIO 50: level=1 fsel=4 alt=0 func=SD0_DAT0
  GPIO 51: level=1 fsel=4 alt=0 func=SD0_DAT1
  GPIO 52: level=1 fsel=4 alt=0 func=SD0_DAT2
  GPIO 53: level=1 fsel=4 alt=0 func=SD0_DAT3
LibreELEC:~ #Mhhh ---- the GPIO18 and 13 are not configured for PWM ....
So I've give it a try:
And ... I've been able to play sound with aplay (after amixer).....
But it's not a real solution ... as the root is squashfs and ro I can not alter the filesystem .....
I would have to do it by my own ....
Will be overwritten by the next update .....
Not a solution 
So I've looked for something different .... and found it:
pwm-audio-pizero/pwm-audio-pi-zero-overlay.dtbo at master · ian57/pwm-audio-pizero · GitHub
I've added the file to the overlay directory and used it by adding:
And now it works 
I've no real idea why the pwm-2chan.dtbo doesn't work, but this solution works and is update resistant.
Thanks a lot for your help!
 
		