use named route and asset in controller

You are using blade tags inside your controller which is not valid. You should use the regular php syntax instead, just like you are doing inside the td. The {{ $variable }} syntax is just sugar code for .

<img src=" .  asset('storage/images/avatar5.png') . ">

<a href=" . route('admin.viewUser', ['id' => $user->id]) . " class="btn d-inline"></a>

<a href="{{ route('admin.viewUser', $user->id) }}" class="btn d-inline"></a> // Does not have to pass a array when its only 1 value

Assets require a bit of digging also the php artisan storage:link has to be used

@Cruorzy i already used php artisan storage:link .. i was using the code in my blade template and it works ..but now i needed to move it to my controller

Oh wouw, you are outpussing html from the controller? Would not have noticed that..

 foreach($users as $user){
         $output .= ' 
          <tr>
             <td >'.$user->id.'</td>
            <td>
            <img src="{{ asset("storage/images/avatar5.png") }}" > //here ?? <-------------
            </td>
            <td>'.$user->name.'</td>                      
            <td>
            <a href="{{route("admin.viewUser",["id"=>'. $user->id .'])}}" class="btn  d-inline">                 
            </a> //here ?? <-------------
            </td>
          </tr>
           ';
        }