Copy ../src/qcad-3.18.1.0/src/3rdparty/qt-labs-qtscriptgenerator-5.9.1 in ../src/qcad-3.18.1.0/src/3rdparty/qt-labs-qtscriptgenerator-5.10.0
rename qt-labs-qtscriptgenerator-5.9.1.pro with qt-labs-qtscriptgenerator-5.10.0
The last comes from qcad bugtracker: FS#1546 : 'Open file' dialog shows no files - although the directory displayed is full of .dxf files, which has a similar issue but is pretty old (2017) and also OS is different, things in common are Dolphin and KDE Plasma, probably both in old versions nowadays.
Once the installation is done, either run the QCAD on Ubuntu using the terminal, you just need to type- qcad or open the Application launcher and there search for it. As its icon appears, click to run the same.
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