In powerpoint, where is defaults for object types stored

I have obviously figured out that to change defaults for object types in Powerpoint, it's posible to right-click object and select change Default.

Where is this setting stored - as PowerPoint does not have the concept of a "normal.dotm" master.

My goal is to somehow set the same for all, or automate the process.

The text default is stored in the theme file. Inside the PPTX file (which is actually a zip file), you'll find a ppt folder and inside that a theme folder and within that, at least a theme1.xml file. There may be more than one themeX.xml file.

In the theme xml file, you'll find this and if you replace the typeface={fontname} with the font name of your choice, you'll change the default font. It'd be wise to get the correct PANOSE number for your new default font and replace that value below also.

<a:objectDefaults>
    <a:txDef>
        <a:spPr>
            <a:noFill/>
        </a:spPr>
        <a:bodyPr wrap="square" rtlCol="0">
            <a:spAutoFit/>
        </a:bodyPr>
        <a:lstStyle>
            <a:defPPr algn="l">
                <a:defRPr dirty="0" smtClean="0">
                    <a:latin typeface="Arial" panose="04020705040A02060702" pitchFamily="82" charset="0"/>
                </a:defRPr>
            </a:defPPr>
        </a:lstStyle>
    </a:txDef>
</a:objectDefaults>