During 1.4R transition that qtwebengine would not build against system-icu. Changing portage/ebuild files had no effect. Emerge of package would always report (-system-icu). Problem was traced with file searching to core-kit/profiles/funtoo/1.0/linux-gnu/package.use.mask/funtoo-use-mask which contained:

# FL-4686: disable system-icu USE flag for the deq-qt/qtwebengine
>=dev-qt/qtwebengine-5.9.2 system-icu

From the Funtoo bug from last year, FL-4686, search found other web references:

• QTBUG-64925 - QtWebEngine 5.9.3 fails to build against system ICU 60.1
• Gentoo Bug 639220 - dev-qt/qtwebengine-5.9.3 with dev-libs/icu-60.1: #error "Update aspirational_scripts per Unicode 10.0"

It appears that original issue was resolved upstream (see https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/220442).

Request reverting suppression of system-icu flag in system profiles going forward.

Until fixed, a workaround is available to build Qt webengine with system-icu flag.
Workaround involves creating a local profile to re-enable. Create directory/file /etc/portage/profile/package.use.mask and populate with:

>=dev-qt/qtwebengine-5.12.0 -system-icu