Screen Time on iPhone showing just "As this device is used, screen time will be reported here."

As parent/guardian I have set extra apple ID for my child under 13 account. I do see it in Settings > Family > his account. And there are settings for screen time and display field where I expected some usage data being shown. Or under Settings > Family > Child's ID > Screen Time .. or there under "See All App & Website Activity".

However neither of these 3 locations show any data. That only shows text "As this device is used, screen time will be reported here".

Thought it might take some time like 24 hours+ to collect anything useful. But it's a week+ and the situation is still the same. Plus it seems that screen time limits are not enforced on child's device as I set them from my device for his one device/account.

Note that child's device has no same iOS version as it's older iPhone8 which cannot get upgraded further.

I just used one of my old ones and re-provisioned it with separate account for a kid. Not truly willing to throw in $1k for a brand new as his first smartphone to break/loose.