Hello mb34,
It appears that you are having an issue with the initial volume setting of your AirPods. The article you came from, How to reset your AirPods Max, has some steps to take if the AirPods are exhibiting abnormal behavior.
Depending on what app is being used, you should be able to go to your iPhone and tap on Settings > Sounds & Haptics to set the volume of the ringer and alerts.
For other volume settings, take a look here: Adjust the volume on iPhone - Apple Support
If the volume settings do not hold, but always go back to full volume, we would test the AirPods with another device. If it happens with the other device, that would indicate an issue with the AirPods. If it does not happen, then that would point towards an issue with the device they are being paired with.
Have a good day.