I I just ran a quick test, and the cookie is setting for me... I used https://experienceleague.adobe.com/docs/analytics/implementation/vars/plugins/getpercentpageviewed.h...
Instead of setting values into props, I just did a console log:

And here is the cookie:

Are you getting a JS error? Did you install the plugin in the proper place, and are you calling it correctly?
Any information you can share about your implementation will help us to help you.