I've now tried installing Craft on multiple PCs to run a local dev environment, but keep getting the same problem. It installs fine, the System Report shows all green, but when I first load the Dashboard I get the message "An unknown error has occurred" and it fails to fetch Craft News items or updates, and then on the Plugin Store it states "The Plugin Store is not available, please try again later."
I've tried playing around with my Apache setup, but honestly I'm not particularly knowledgeable in that area.
All PCs have been running Windows 10, the latest version of WAMP server, PHP 7.2, and "latest" version of Craft (though it's now two installs behind, which is why I know the updates aren't working despite stating that I'm "up to date").
Live version of the site is working perfectly after upload via FTP, and I've tried reinstalling several times.