So the "Head Tracked" option should actually appear in Control Center rather than the AirPods settings screen you've screenshotted.
Check this:
Long press the volume slider in Control Centre while something is playing - you should see Spatial Audio at the bottom right, and tapping it should give you three options: Off, Fixed, and Head Tracked.
If Head Tracked still isn't there, check this: go to Settings, tap your AirPods name at the top, scroll down to Accessibility, and make sure "Follow iPhone" is turned on. That's the switch that enables head tracking and it sometimes gets toggled off.
Also worth knowing - head tracking is saved per app. So if it was previously set to Fixed in Music, it'll stay that way each time you open Music. Check if it's missing in all apps or just one.