The QtGraphicalEffects module has been deprecated and is no longer part of Qt.
The functionality of the module has been partially incorporated into the Qt5Compat module.
The documentation for those parts can be found at Qt 5 Compatibility APIs: Graphical Effects
To work on patches for the Qt 5 series, check out a local branch of the relevant Qt version, e.g.:
$ git checkout 5.15
Branch '5.15' set up to track remote branch '5.15' from 'origin' by rebasing.
Switched to a new branch '5.15'To inspect the code in the dev branch prior to its removal, follow these steps:
$ git checkout -b my-dev dev~1
Switched to a new branch 'my-dev'