The mirror I see in the UK does not have the image for KDE plasma yet.
This is the URL https://mirror.ufdroht.net/fedora/fedora/linux/releases/test/45_Beta/KDE/x86_64/iso/Fedora-KDE-Desktop-Live-45_Beta-1.3.x86_64.iso from Fedora KDE Plasma Desktop | The Fedora Project