PlayOn on the PC is on life support at this point it seems. It uses Internet Explorer and may still have dependencies on Flash, though I think that was more a provider dependency.
It's very fragile and almost like they use Selenium or some other automation tester for UI then just screen cap the whole thing. I say this because it breaks frequently when providers change their UI.
Plugins constantly come and go and stop working.
They amount of support required to keep it going is tremendous and they're pushing the cloud as a service to support and maintain it.
With their software, you can record Netflix/Hulu/Peacock/Disney+/Whatever to your computer or stream videos from those services to a Kodi box. They've never been sued from any of these services because of their (interesting) legal argument.
If you could integrate their services or techniques, you wouldn't need any approval from the streaming services.