why is there no app tab on desktop

Renaming or deleting the OOBE file should fix the issue.  There's usually a file within the OOBE folder called "ServiceConfig.xml" that has AppsPanel <visible> set to false.  By either removing the OOBE folder completely or updating the xml file to read as "true" generally corrects the issue allowing the Apps panel to now display.

Alternatively the xml file can be modified manually.

Following are the steps to retroactively enable the Apps panel:

Locate the ServiceConfig.xml file.

Windows: C:\Program Files (x86)\Common Files\Adobe\OOBE\ Configs\ServiceConfig.xml

Mac OS: /Library/Application Support/Adobe/OOBE/Configs/ServiceConfig.xml

In the file, locate the <visible> element and change its content to True (Default is False).

<config>

    <panel>

        <name>AppsPanel</name>

        <visible>false</visible>

    </panel>

</config>