Yes, as Jakub mentioned Xdebug is coming from our feed. Since you've mentioned you are trying to run WebPI manually. You could try to add our custom feed through WebPi GUI app and you will be able to install the packages provided by us.
As for the issue, we suspect some dependencies coming from the primary feed might be failing to download for some reason. To test this you can just try to install PHP 8.0 (e.g. directly from PHP Tools). It's from us without many other dependencies. If this would work we'd know it's an issue with some dependency coming from the official feed.
Anyway, we will provide much more logs in the next update so it will be easier to diagnose issues like this.