1

Replace Default Qt version paths in:

/usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf:

/opt/Qt5/bin
/opt/Qt5/lib

Check:

qtchooser -print-env

2

PATH set

export PATH=/path/to/bin:$PATH

Reference:

Qt5 installation and path configuration

How to change default used version of Qt/qmake?