Please add sleep score onto Venu SQ

Assuming you have the original Venu Sq. Garmin doesn't typically add features to a watch that is over 4 years old. However, you can request it here -Share Ideas | Garmin 

I don't expect the feature to be added to the watch but to the garmin connect app. 

The feature already is in Garmin Connect, assuming that your watch supports it. The score is calculated by the watch, not on the app. In fact, most of the data processing is done by the devices, and very little is done by the app. GC is merely a viewer of the data loaded from the watch. Hence if you want to see the Sleep Score, you really need a watch having the feature.