I have a confusion  about an idiom
Is “a little bit of everywhere  and unlike anywhere” an idiom？ and what does it mean

No, it isn't an idiom. An idiom is a phrase used with a non-literal meaning which you can't guess without knowing the idiom.

I have never heard this phrase before, but it's clear what it means. It sounds like someone is commenting on the style of a particular place. The designers have copied aspects of many locations (eastern, western, traditional, modern) but the result is something original.  For example, this place has aspects of Paris, Dubai and New York, but it doesn't look like any of those places.