QtWebEngine/Qt6Build
Building Qt6 WebEngine from Source
Please check platform notes for required dependencies https://doc.qt.io/qt-6/qtwebengine-platform-notes.html.
Qt builds can be done in top level manner, meaning that you clone qt5 main repository (git://code.qt.io/qt/qt5.git), which then initializes all the qt modules as sub-modules,configures and builds everything in one go. However, this small guide shows the alternative way, so called module build, which is more robust as it clones minimum subset of modules required for QtWebengine and compiles each module separately. It is also very flexible way of building as you can try to compile newer QtWebengine module with older qt modules.
Obtain Qt6 sources code
mkdir qt6
cd qt6
git clone git://code.qt.io/qt/qtbase.git
git clone git://code.qt.io/qt/qtshadertools.git
git clone git://code.qt.io/qt/qtdeclarative.git
git clone git://code.qt.io/qt/qtwebengine.git
cd qtwebenigne
git submodule init
git submodule update
cd ..
Note that web engine needs initialization of submodule.
Select branches
Let's assume we want to compile Qt 6.4.3 with Qt Webengine 6.5.0 Therefore, in qtbase, qtshadertools, qtdeclarative repositories we select barnches:
git checkout origin/6.4.3
Where-else in qtwebengine
cd qtwebengine
git checkout origin/6.5.0
git submodule update
cd ..