Hi yiel,
Sounds like you've covered a good bit of the troubleshooting steps which normally resolve this issue. Have you tried pairing your AirPods with another iOS device? By pairing them with another iOS device you'll be able to see if the settings appear like shown in this article: Adjust the settings of your AirPods.
If the settings appear on the other iOS device, then you'll know that the issue is isolated to the iOS On your iPhone. This can be resolved by reinstalling the iOS. Before any reinstall, be sure that you have a current backup of your iPhone data. Having a backup of your data is like having an insurance policy, you don’t plan on using it, but it’s great to have if you need it. These are the steps to follow to create a backup if you haven't already done so: How to back up your iPhone, iPad, and iPod touch.
Once you have the backup, follow the steps from this article: If you can't update or restore your iPhone, iPad, or iPod touch. Be sure when you reach step 4 you select Update. By selecting Update iTunes will try to reinstall the iOS without erasing your data.
If you set up your AirPods with another device, and the settings still do not appear, Contact Apple Support.
Cheers