CreateAPaymentMethodOnlyVisibleInAdmin

config.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
    <default>
        <payment>
            <admin_only>
                <active>1</active>
                <title>Admin Payment Only</title>
                <order_status>pending</order_status>
                <allowspecific>0</allowspecific>
                <can_use_internal>1</can_use_internal>
                <can_use_checkout>0</can_use_checkout>
                <is_offline>1</is_offline>
                <model>MageVision\Blog78\Model\AdminOnly</model>
                <group>offline</group>
            </admin_only>
        </payment>
    </default>
</config>