Not greyed out. The toggle just doesn't... toggle. (Screen record attached)
I think Clear Calling is still exclusively on the Pixel 7. It's supposed to roll out later for earlier Pixels: https://techcrunch.com/2022/12/05/g...RJuGTFRVNnxz2RrypLws7Lq56PVxy5-A1rpqVBF5k8BmQ
It may be that they jumped the gun including it in the Pixel Tips app on the Pixel 6. Do you actually see the setting in Settings>Sound & Vibration?