In a previous question (https://tex.stackexchange.com/questions/548738/special-character-oe-and-biblatex-with-xelatex), it was proposed to modify a part of the code to solve the problem. But the new code seems to be not compatible with the block code in the preamble relative to titlepage (which comes from Tufte-book documentclass). This block code is indicated "NEW" in the MWE above. This Bock code prevents compilation with XeLateX and leads to an error message: Package soul Error.
\RequirePackage{luatex85}
\documentclass[nobib,symmetric,justified,marginals=raggedouter]{tufte-book}
\usepackage{fontspec}
\setmainfont{fbb}
\usepackage{microtype}
\usepackage{fancyvrb}
\newcommand{\plainsubtitle}{}% plain-text-only subtitle %NEW
\newcommand{\subtitle}[1]{% NEW
\gdef@subtitle{#1}% NEW
\renewcommand{\plainsubtitle}{#1}% use provided plain-text title %NEW
\ifthenelse{\isundefined{\hypersetup}}% NEW
{}% hyperref is not loaded; do nothing% NEW
{\hypersetup{pdftitle={\plaintitle: \plainsubtitle{}}}}% set the PDF metadata title %NEW
}
\renewcommand{\maketitlepage}[0]{% NEW
\cleardoublepage% NEW
{% NEW
\ssffamily% NEW
\begin{fullwidth}% NEW
\fontsize{18}{20}\selectfont\par\noindent\textcolor{darkgray}{\allcaps{\thanklessauthor}}% NEW
\vspace{11.5pc}% NEW
%\fontsize{36}{40}\selectfont\par\noindent\textcolor{darkgray}{\allcaps{\thanklesstitle}}% NEW
\fontsize{30}{32}\selectfont\par\noindent\textcolor{darkgray}{\allcaps{\thanklesstitle}}% NEW
\vspace{3pc}% NEW
\fontsize{25}{27}\selectfont\par\noindent\textcolor{darkgray}{\allcaps{\plainsubtitle}}% NEW
\vfill% NEW
\fontsize{14}{16}\selectfont\par\noindent\allcaps{\thanklesspublisher}% NEW
\end{fullwidth}% NEW
}% NEW
\thispagestyle{empty}% NEW
\clearpage% NEW
}% NEW
\makeatother % NEW
\title{The Title}% NEW
\subtitle{The subtitle}% NEW
\author{From me} % NEW
\publisher{Editor}% NEW
\usepackage{csquotes}
\usepackage[backend=biber, style=authoryear-icomp]{biblatex}
\makeatletter
\newbibmacro{adtcite}{%
\iffieldundef{shorthand}
{\ifthenelse{\ifciteibid\AND\NOT\iffirstonpage}
{\usebibmacro{cite:ibid}}
{\iffieldequals{namehash}{\cbx@lasthash}
{\setunit{\compcitedelim}}
{\printnames{labelname}%
\setunit{\printdelim{nameyeardelim}}%
\printlabeldateextra
\setunit{\printdelim{nametitledelim}}%
\savefield{namehash}{\cbx@lasthash}}%
\usebibmacro{cite:title}}}%
{\usebibmacro{cite:shorthand}%
\usebibmacro{cite:reinit}}%
\setunit{\multicitedelim}}
\makeatother
\newbibmacro{cite:title}{%
\printtext[bibhyperref]{\printfield[citetitle]{labeltitle}}}
\DeclareCiteCommand{\fadtcite}[\mkbibfootnote]
{\usebibmacro{cite:init}%
\usebibmacro{prenote}}
{\usebibmacro{citeindex}%
\usebibmacro{adtcite}}
{}
{\usebibmacro{cite:postnote}}
\DeclareMultiCiteCommand{\fadtcites}[\mkbibfootnote]{\fadtcite}{\setunit{\multicitedelim}}
\DeclareAutoCiteCommand{fadt}{\fadtcite}{\fadtcites}
\ExecuteBibliographyOptions{autocite=fadt}
\usepackage{mdframed}
\newmdenv[skipabove=3.5ex plus 1ex minus .2ex,% Equal to section title spacing
innerleftmargin=0pt,innerrightmargin=0pt,%
innerbottommargin=0pt,innertopmargin=0pt,linewidth=0pt,innermargin=0pt,%
outermargin=\dimexpr-\marginparwidth-\marginparsep\relax]{mdfullwidth}
\defbibenvironment{bibliography}
{\list{}{\parsep\bibparsep}}
{\endlist}
{\item}
\AtEveryBibitem{\hskip-\bibhang}
\begin{filecontents}{\jobname.bib}
@BOOK{Buchet,
author = {Buchet, Edmond},
title = {Jean-S'{e}bastien Bach. L'\oe uvre et la vie.
Deux si`{e}cles d''{e}tudes et de t'{e}moignages},
year = {1963},
publisher = {'{E}ditions Les Libraires Associ'{e}s},
place = {Saverne},
pagetotal = {267},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\begin{document}
\frenchspacing% NEW
% Front matter
\frontmatter% NEW
\maketitle% NEW
\cleardoublepage% NEW
% r.1 blank page
\blankpage% NEW
% r.3 full title page
\maketitle% NEW
\cleardoublepage% NEW
% r.1 blank page
\blankpage% NEW
\newthought{How to fix} the problem with "\oe uvre"\autocite[42]{Buchet}?
\begin{fullwidth}
\bibhang=0pt
\printbibliography
\end{fullwidth}
\end{document}
Thanks for your help to solve the problem.
\ssffamilyseems to be a typo for\sffamily. But fixing that does not resolve all the other errors one gets. – moewe Jun 16 '20 at 20:26\renewcommand{\allcaps}[1]{\expandafter\allcapsspacing\expandafter{\MakeTextUppercase{#1}}}% \renewcommand{\smallcaps}[1]{{\scshape\expandafter\smallcapsspacing\expandafter{\MakeTextLowercase{#1}}}}%– moewe Jun 16 '20 at 20:42