Hi,
Problem is solved 
@Ulf My headphones work correctly with other devices. So the issue seems to be related to my phone.
I try with an other Pixel 5 whixch is also with /e/OS and it works with my headphones and my adapter.
So I check the usb configuration between the 2 phones and found 1 difference. My phone is in French so here is the option (in the “Confidentialité > Trust” menu):
Restreindre l’USB
Contrôler la prise en charge des connexions USB telles que les écouteurs, les périphériques de stockage, etc.
On my phone this was set to:
Autoriser les connexions USB lorsque l’appareil est déverrouillé
On the other it was:
Toujours autoriser les connexions USB
I change the setting on my phone and now it works!
Thank you for your help