wp schrieb:
How many civil airports in Europe are closed for ultralight aircrafts?
If so, what's the common cause?

To be more precise: which international airports you are aware of are
closed for ultralights? I wonder if this is common practice or just an
exception?

Again: When it comes to ultralights, there is no such thing as "Europe".

In terms of ultralight in mean LSA/VLA of MTOW 495/600kg.

Even this definition is not unified in Europe.