That type of bird is a male Bluethroat.
Male Bluethroats from Alaska to northern Europe have red centers to the blue throat. Those in central and southern Europe have white throat centers or entirely blue throats.
The male Bluethroat is quite striking with its blue and red throat and its flashing reddish tail. However, it normally is very secretive and hard to see as it skulks through thick vegetation. It is easy to see only while it is singing or performing flight displays
https://www.allaboutbirds.org/guide/Bluethroat/overview
Do we have any secretive male suspects in central or Southern Europe? That would include the UK, Poland, Germany, France, and Slovakia.
Just to clarify my reasoning, Q could have picked a picture of any bird for his “When does a bird sing.” post. Why a bluethroat?
Because a male, Central European is singing? Someone in the UK?
The Blue Throat mimics other birds