Steps to reproduce the issue

create a SEF url with Route::_ like this:

Route::_('index.php?option=com_example&task=payment.response&processor=paylater&order=1234567890&test1=123&test2=456', true, Route::TLS_IGNORE, true)`

the router builds the following URL:

[yourdomain]/nl/sub/payment-page/payment/response?processor=paylater&order=1234567890&test1=123&test2=456

now in the site controller for com_example do a var_dump for: \Jooma\Input\Input

Expected result

The extra query parameters (order, test1, test2) should be part of the data (retrievable with getString)

Actual result

Joomla 3: this works okay as the following data is in Input:

protected 'data' => 
    array (size=12)
      'processor' => string 'paylater' (length=8)
      'amp;order' => string '1234567890' (length=10)
      'amp;test1' => string '123' (length=3)
      'amp;test2' => string '456' (length=3)
      'language' => string 'nl-NL' (length=5)
      'order' => string '1234567890' (length=10)
      'test1' => string '123' (length=3)
      'test2' => string '456' (length=3)
      'Itemid' => string '4490' (length=4)
      'option' => string 'com_example' (length=20)
      'task' => string 'payment.response' (length=16)
      'lang' => string 'nl-NL' (length=5)

On Joomla 4 however this will fail as the data is not fully stored / converted, as you can see below only the (e.g. 'amp;order' is stored and not 'order' so trying to getString('order') will fail

protected 'data' => 
    array (size=4)
      'processor' => string 'paylater' (length=8)
      'amp;order' => string '1234567890' (length=10)
      'amp;test1' => string '123' (length=3)
      'amp;test2' => string '456' (length=3)

System information (as much as possible)

Additional comments

workaround (or better solution) is not to use \Joomla\Input\Input but Factory::getApplcation()->input as this works correct in both Joomla 3 and Joomla 4