This is a follow up to this post. With either of the proposed solutions, this causes a conflict. Namely, the thumb for the phantom section, in this case 'Index', will show the last chapter. How can I make it show 'Index' or nothing?
\clearpage
\pagestyle{empty}
\phantomsection
\addcontentsline{toc}{chapter}{Index}
\label{index}
\chapter*{Index}
Here's the full code for the first solution:
\documentclass[oneside]{scrbook}
\usepackage{fontawesome}
\usepackage[french]{babel}
\usepackage{/usr/local/texlive/2018/texmf-dist/doc/latex/koma-script-examples/Anhang-B/source/chapterthumb}
\usepackage{csquotes}
\usepackage[T1]{fontenc}
\usepackage{lipsum}
\usepackage{scrlayer-scrpage}
%\AddLayersToPageStyle{@everystyle@}{chapterthumb}
%\addtokomafont{chapterthumb}{\bfseries}
\newpairofpagestyles[scrheadings]{part}{}
\renewcommand\partpagestyle{plain.part}
\AddLayersToPageStyle{scrheadings}{chapterthumb}
\AddLayersToPageStyle{plain.scrheadings}{chapterthumb}
\addtokomafont{chapterthumb}{\bfseries}
\usepackage{hyperref}
\begin{document}
\part{Foo}
\chapter{Pas du tout}
\lipsum[1]
\chapter{Un peu}
\lipsum[2]
\pagestyle{empty}
\part{Bar}
\chapter{Beaucoup}
\lipsum[3]
\chapter{Passionnément}
\lipsum[4]
\clearpage
\pagestyle{empty}
\phantomsection
\addcontentsline{toc}{chapter}{Index}
\label{index}
\chapter*{Index}
\end{document}
And for the second:
\documentclass[oneside]{scrbook}
\usepackage{fontawesome}
\usepackage[french]{babel}
\usepackage{/usr/local/texlive/2018/texmf-dist/doc/latex/koma-script-examples/Anhang-B/source/chapterthumb}
\usepackage{csquotes}
\usepackage[T1]{fontenc}
\usepackage{lipsum}
\usepackage{scrlayer-scrpage}
%\AddLayersToPageStyle{@everystyle@}{chapterthumb}
\addtokomafont{chapterthumb}{\bfseries}
\newpairofpagestyles[scrheadings]{part}{}
\renewcommand\partpagestyle{plain.part}
\AddLayersToPageStyle{scrheadings}{chapterthumb}
\AddLayersToPageStyle{plain.scrheadings}{chapterthumb}
\addtokomafont{chapterthumb}{\bfseries}
\usepackage{hyperref}
\begin{document}
\part{Foo}
\chapter{Pas du tout}
\lipsum[1]
\chapter{Un peu}
\lipsum[2]
\pagestyle{empty}
\part{Bar}
\chapter{Beaucoup}
\lipsum[3]
\chapter{Passionnément}
\lipsum[4]
\clearpage
\pagestyle{empty}
\phantomsection
\addcontentsline{toc}{chapter}{Index}
\label{index}
\chapter*{Index}
\end{document}

