AirPods case not showing up

Most of the time that is normal behavior, it depends on where you are looking:

Battery pop-up or Batteries widget: the case only reports its charge when it can talk to the phone, which means the lid open, at least one AirPod inside the case, and the case near your iPhone. A closed case with both buds out stays silent, so only the two buds show their levels. Put both buds in, open the lid next to the phone, and the case percentage appears. If the case battery is completely dead it also will not appear until it has charged for a few minutes.

Find My: only the newer cases can be tracked on their own. The AirPods Pro 2 MagSafe case (and AirPods 4 cases) show up as their own item and can play a sound. On older models the case has no tracker of its own, Find My locates the AirPods themselves, and the case is found wherever the buds last were. If yours is one of the older cases, it will never appear as a separate item, that part is by design.

I'm using the new one case (Airpods 4 ANC) but it still doesn't show them to me separately.After I reset it, the case appears, but then it switches back to the headphones.