Then /usr/lib/x86_64-linux-gnu/pkgconfig/Qt5Help.pc is already present. Why did you create it manually?
https://packages.ubuntu.com/bionic/amd64/qttools5-dev/filelist
In your manually created file the include path is wrong. You need to replace -I${includedir}/QtGui with -I${includedir}/QtHelp.
Then /usr/lib/ x86_64- linux-gnu/ pkgconfig/ Qt5Help. pc is already present. Why did you create it manually?
https:/ /packages. ubuntu. com/bionic/ amd64/qttools5- dev/filelist
In your manually created file the include path is wrong. You need to replace -I${includedir} /QtGui with -I${includedir} /QtHelp.