Schengen considers arrivals from the US , arrivals from the uk, and arrivals from other schengen countries as clean, so no requirement to reclear security if the airport makes that possible and you can be kept clean.

if you cannot be kept clean then you will need to clear security.

This can lead to inconsistent arruval process deoending where in the airport you disembark (eg at fra)

The uk only considers uk domestic as clean, so any international arrival needs to reclear security.