The source tarball (.tar.gz) does not include the git submodule dependencies, more specifically pugixml and SingleApplication. This results in a warning with qmake:
$ qmake-qt5
Info: creating stash file /home/nicola/sandbox/aur/qeletrotech/src/qelectrotech-source-mirror-0.100/.qmake.stash
Cannot read .../SingleApplication/singleapplication.pri: No such file or directory
and subsequent errors during make:
$ make
...
In file included from sources/bordertitleblock.h:22,
from sources/bordertitleblock.cpp:18:
sources/diagramcontext.h:20:10: fatal error: pugixml/src/pugixml.hpp: No such file or directory
20 | #include "pugixml/src/pugixml.hpp"
| ^~~~~~~~~~~~~~~~~~~~~~~~~
| 