Why not just use eloquent?
$student = User::where('usertype','=','student')
->with('supervisor')
->get();
and
@foreach ($submitted as $project)
<tr>
<td>{{++$sno}}</td>
<td>{{$student->firstname}} {{$student->lastname}}</td>
<td>{{$student->supervisor->name ?? 'No supervisor'}}</td>
</tr>
@endforeach
For it to work you need to add this to the User model
public function supervisor()
{
return $this->belongsTo(User::class, 'supervisor_id');
}