You can answer that EndeavourOS uses the Arch repositories, so it does the same as Arch.
It is the alpha release, not the git version:
source=(https://download.kde.org/unstable/plasma/$_dirver/$pkgname-$pkgver.tar.xz{,.sig})
source=(https://download.kde.org/unstable/frameworks/$pkgver/$pkgname-$pkgver.tar.xz{,.sig})