I created a solution with a seperate function

In my user model:

    public function allroles()
    {
        //
        $roles=Role::select('id','name','filename','description')->get();
        foreach ($roles as $role) {
            $ru=RoleUser::select('id')
            ->where('user_id','=',$this->id)
            ->where('role_id','=',$role->id)
            ->count();
            if($ru){
                $role->selected=TRUE;
            }else{
                $role->selected=FALSE;
            }
            $data[]=$role;
        }
        
        return $data;
    }

To call this function in my eloquent model (Employee has one user ...)

So in my EmployeeController:

$e=Employee::where('id','=',$id)->with('user')->first(); 
//I add it to the object
$e->roles=$e->user->allroles();

But maybe it can be done easier? With a direct eloquent function?

Maybe you colud use a union of those having it true and false.

$yes = $this->roles()->select(DB::Raw('*, TRUE as extra');//don't get
$no = Roles::select(DB::Raw('*, FALSE as extra')->whereNotIn('id', function($query){
$query->select('role_id')->from('role_user')->where('user_id', $this->id);
});//don't get
return $yes->union($no)->get();//get now