Wrong Download Links (https://binary-factory.kde.org/)
As mentioned and fixed in Kate the KDevelop has the same issue: utilities/kate#117 (closed)
The download links on https://kdevelop.org/de/download/ link all to https://binary-factory.kde.org/ and it is not possible to download the packages. Unfortunately it is not possible to install KDevelop on macOS or Windows as the links are dead.
Maybe you can also ping other KDE developers to check for their applications.