/usr/bin/kubuntu-devel-release-upgrade is in ubuntu-release-upgrader-qt 1:18.04.17.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 | #!/bin/sh
pkexec do-release-upgrade -m desktop -f DistUpgradeViewKDE -d
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