Yes I agree that jurplel/install-qt-action may be overriding the manual install of qt & qwt.
Here is the build output when I remove jurplel/install-qt-action from build.yml -


Linux
Qt Code: 
  1. Run qmake -set QMAKEFEATURES /resources/qwt/
  2.   qmake -set QMAKEFEATURES /resources/qwt/
  3.   qmake PowerVelo.pro
  4.   shell: /bin/bash -e {0}
  5. Info: creating stash file /home/runner/work/MaximumTrainer/MaximumTrainer/.qmake.stash
  6. /home/runner/work/MaximumTrainer/MaximumTrainer/PowerVelo.pro:6: 'versionAtLeast' is not a recognized test function.
  7. Project ERROR: Use at least Qt version 5.12
  8. Error: Process completed with exit code 3.
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looking into this it appears that QT 5.9.5 was installed, so I have just adjusted the pro file build for the moment

Mac
Qt Code: 
  1. 0s
  2. Run qmake -set QMAKEFEATURES /resources/qwt/
  3.   qmake -set QMAKEFEATURES /resources/qwt/
  4.   qmake PowerVelo.pro
  5.   shell: /bin/bash -e {0}
  6. /Users/runner/work/_temp/eb005e71-d79b-4b46-a79a-086122d1c270.sh: line 1: qmake: command not found
  7. Error: Process completed with exit code 127.
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Reading this implies a path issue to me.


In my latest build I have removed jurplel/install-qt-action as this is causing a conflict & here are the latest errors -

Linux
Qt Code: 
  1. Run qmake -version
  2. QMake version 3.1
  3. Using Qt version 5.9.5 in /usr/lib/x86_64-linux-gnu
  4. Info: creating stash file /home/runner/work/MaximumTrainer/MaximumTrainer/.qmake.stash
  5. /home/runner/work/MaximumTrainer/MaximumTrainer/PowerVelo.pro:6: 'versionAtLeast' is not a recognized test function.
  6. Project ERROR: Use at least Qt version 5.9.0
  7. Error: Process completed with exit code 3.
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Mac this is back to the qwt not found error, not sure if this is as brew install qwt6 by default
Qt Code: 
  1. In file included from src/_db/userdao.cpp:4:
  2. src/main/util.h:7:10: fatal error: 'qwt_plot.h' file not found
  3. #include <qwt_plot.h>
  4.          ^~~~~~~~~~~~
  5. 1 error generated.
  6. make: *** [build/release/.obj/userdao.o] Error 1
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full build can be found https://github.com/MaximumTrainer/MaximumTrainer/actions/runs/298838171