what does it mean "not working"? seems fine, just one thing is, that you define the prefix twice.
one here in bootstrap/app.php:
...
then: function () {
Route::namespace('Admin')
->prefix('admin') //<- here
->name('admin.')
->group(base_path('routes/admin.php'));
},
and here too in routes/admin.php:
Route::group(['prefix' => 'admin', 'middleware' => 'guest:web', 'namespace' => 'Admin'] //<- here and below in your code for the second group too
the links then will be like this:
/admin/admin/login
/admin/admin/logout
/admin/admin/developer
...
what it the output when you run php artisan route:list command?