What I am trying to do is to display option like below screenshot in my custom offline payment module:

However, the red box is not appearing on my offline payment method option inside the admin store>configuration>payment method> custom payment
My code in system.xml file is as below:
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
<system>
<section id="payment">
<group id="offlinepaymentext" translate="label" sortOrder="2" showInDefault="1" showInWebsite="1" showInStore="1">
<label>Offilne Payment Extension</label>
<field id="active" translate="label comment" sortOrder="1" type="select" showInDefault="1" showInWebsite="1" showInStore="0">
<label>Enable</label>
<source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
</field>
<label>New Order Status</label>
<field id="order_status" translate="label" type="select" sortOrder="20" showInDefault="1" showInWebsite="1" showInStore="0" canRestore="1">
<label>Pending</label>
<source_model>Magento\Sales\Model\Config\Source\Order\Status\Pending</source_model>
</field>
</group>
</section>
</system>
</config>
Also, I don;t want NewProcessing or processing but instead of I want Pending status inside the dropdown.
My config.xml file look like below:
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../Store/etc/config.xsd">
<default>
<payment>
<offlinepaymentext>
<payment_action>capture</payment_action><!-- You can use another methor like capture -->
<model>OfflinePayment\Ext\Model\PaymentMethod</model>
<active>1</active>
<title>Offline Payment</title>
<order_status>pending</order_status><!-- set default order status pending_payment-->
</offlinepaymentext>
</payment>
</default>
</config>
I am new to magento 2 and don't know how to add this option in my custom payment module.
after making all the above changes my admin section of magento display like below(admin>stores>configurations>Sales>PAyment Methods)

Any idea? what I am doing wrong here?