libicudata is bundled with calibre look in /opt/calibre/lib there is no need ot install it. Why webengine is not picking it up, I am not sure, probably sandboxing. You could try symlinking them into /usr/lib or /usr/local/lib to see if it works around the issue. Or turn off sandboxing as decribed here:
https://doc.qt.io/qt-6/qtwebengine-debugging.html