Hawaiian license plate for electric vehicles, 8W40.
The only cybertruck I've seen personally in Europe.

Rear:

In general I thought it was not legal in europe due some issues like pedestrian safety. With Hawaii plates I wonder if that's someone in the US military who transferred and had their vehicle shipped over?

There are a few registered in Europe, I've seen pictures of some on Polish, Czech and Albanian plates.
There's also a Swiss company trying to build them conform to European standards.
But other than that you're right, they're mostly not legal. That's why it's on a trailer, probably. Possibly imported for events or stuff like that.

With Hawaii plates I wonder if that's someone in the US military who transferred and had their vehicle shipped over?

I can only speak for Germany; the US forces are usually permitted to import and use vehicles that couldn't get a registration if e.g. a German imported them like that (not without further modifications). However for the cybertruck specifically, German declined to register them.
Personally, I'm quite happy about that. That's really not a vehicle I want to see driving on our roads.