<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <tab id="tinify" translate="label" sortOrder="10">
            <label>Tinify</label>
        </tab>
        <section id="tinify_compress_images" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
            <label>PNG and JPEG compression</label>
            <tab>tinify</tab>
            <resource>Tinify_Compress_Images::tinify_compress_images</resource>
            <group id="general" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="0" showInStore="0">
                <label>Configure PNG and JPEG image compression</label>
                <field id="key" translate="label comment" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>TinyPNG API key</label>
                    <comment><![CDATA[Visit <a href="https://tinypng.com/developers" target="_blank">TinyPNG Developer section</a> to to get an API key.]]></comment>
                </field>
            </group>
        </section>
    </system>
</config>

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <section id="tinify_compress_images" translate="label" type="text" sortOrder="20" showInDefault="1" showInWebsite="1" showInStore="1">
            <label>Image Compression</label>
            <tab>general</tab>
            <resource>Tinify_Compress_Images::tinify_compress_images</resource>
            <group id="general" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="0">
                <label>Configure PNG and JPEG image compression</label>
                <field id="key" translate="label comment" type="text" sortOrder="10" showInDefault="1" showInWebsite="0" showInStore="0">
                    <label>TinyPNG API key</label>
                    <comment><![CDATA[Visit <a href="https://tinypng.com/developers" target="_blank">TinyPNG Developer section</a> to to get an API key.]]></comment>
                </field>
            </group>
        </section>
    </system>
</config>

Move config to General tab.
Move config to General tab.
