Implement backend model of single_store_mode/enabled for the purpose of extensible

First of not not sure about its feature or not.
Point - Below field should have Back-end model in vendor\magento\module-backend\etc\adminhtml\system.xml so one can extend the class to address the any issue on the third-party/custom module level.

Field - single_store_mode/enabled

<group id="single_store_mode" translate="label" type="text" sortOrder="150" showInDefault="1" showInWebsite="0" showInStore="0">
                <label>Single-Store Mode</label>
                <field id="enabled" translate="label comment" type="select" sortOrder="10" showInDefault="1" showInWebsite="0" showInStore="0">
                    <label>Enable Single-Store Mode</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                    <comment>This setting will not be taken into account if system has more than one store view.</comment>
                </field>
 </group>

Possible backend model

<backend_model>Magento\Config\Model\Config\Backend\SingleStoreMode</backend_model>

The idea to implement backend_model is that any backend model extends the Magento\Framework\App\Config\Value which will be having enough methods such as isValueChanged and getOldValue and afterSave and afterDelete .

Based on this
https://github.com/magento/magento2/issues/25933
https://github.com/magento/magento2/issues/22344

Start with vendor\magento\module-backend\etc\adminhtml\system.xml and the single_store_mode/enabled field. Read the proposed Magento\Config\Model\Config\Backend\SingleStoreMode entry and the related issues #25933 and #22344 to understand the intended behavior. Done means the field has an extensible backend model with the lifecycle methods described in the issue.