Hi @juzzlin, desktop-qt5 in your snapcraft.yaml is a so-called “remote” part. Those are no longer supported in snapcraft due to complexity with regards to different snap bases. The replacement are (much more flexible) extensions, but they’re not ready yet for Qt5.
In the mean time, you can just bring the desktop-qt5 part into your snapcraft.yaml - have a below for an example on how to do it.