Using WAMP, trying to create a plugin, getting error: You do not have sufficient permissions to access this page

administrator isn’t a capability, it is a role, so the reason you get that error is because WordPress doesn’t recognizes the capability you gave.

If you look up the capabilities of the administrator role, you can see that the administrator is the only one with the capability manage_options. This is the one you should use.

So what you can do is change the capability to manage_options:

add_options_page( __( 'Theme Options' ), __( 'Theme Options' ), 'manage_options', __FILE__, function() {
    echo 'Hello';
} );

Hope it helps!