Fortunately, upstream has an 'engine' branch they are working on.
As stated in the release page of v0.9.14, it is the last version to support QtWebKit. Will wait for next release to update to QtWebEngine.
0.9.15 released: https://github.com/Sigil-Ebook/Sigil/releases
The bug has been referenced in the following commit(s):
Author: Zamarin Arthur <email@example.com>
AuthorDate: 2019-07-21 05:44:15 +0000
Commit: Andreas Sturmlechner <firstname.lastname@example.org>
CommitDate: 2019-07-21 11:58:34 +0000
app-text/sigil: bump v0.9.16
Package-Manager: Portage-2.3.69, Repoman-2.3.16
Signed-off-by: Zamarin Arthur <email@example.com>
Signed-off-by: Andreas Sturmlechner <firstname.lastname@example.org>
app-text/sigil/Manifest | 1 +
app-text/sigil/sigil-0.9.16.ebuild | 96 ++++++++++++++++++++++++++++++++++++++
2 files changed, 97 insertions(+)