Are the Packages etoolbox and scrextend Incompatible? (Trying to Increase Horizontal Space Between Bold Footnotemarks and Their Text)

Question

This question is an extension of How to Make Bold the Footnotemarks Appearing After the Footnote Line

Starting with the code from Werner's excellent answer which makes bold the footnotemarks after the footnote line, I am adding

\usepackage{scrextend}
\deffootnote[.35in]{.5in}{.195in}{\makebox[.5in][r]{\thefootnotemark.\hspace{.1in}}}

to augment the space between the bold footnotemarks and their associated text.

However, when I run the code

\documentclass{book}
\usepackage{etoolbox}

\makeatletter
\patchcmd{\@makefntext}% <cmd>
  {\@makefnmark}% <search>
  {\let\normalfont\bfseries\@makefnmark}% <replace>
  {}{}% <success><failure>
\makeatother

\usepackage{scrextend}
\deffootnote[.35in]{.5in}{.195in}{\makebox[.5in][r]{\thefootnotemark.\hspace{.1in}}}
\begin{document}
\noindent A sentence.\footnote{Footnote A.}
Another sentence.\footnote{Footnote B.}
Another sentence.\footnote{Footnote C.}
\end{document}

I get the spacing adjustment I am looking for---but the footnotemarks are no longer bold.

Remark: I have discovered that when I run Werner's code with only the package scrextend added, the footnotemarks are no longer bold:

QUESTION: Are the packages etoolbox and scrextend incompatible? (and) How may I increase the horizontal spacing between each footnotemark and its text for each such mark below the footnote line?

Thank you.

Answer 1

\deffootnote redefines the footnote code and so overwrites also your patch. But you can add the bold font simply to the definition there:

\documentclass{book}
\usepackage{etoolbox}

\usepackage{scrextend}
\deffootnote[.35in]{.5in}{.195in}{\makebox[.5in][r]{\bfseries\thefootnotemark.\hspace{.1in}}}

\begin{document}
\noindent A sentence.\footnote{Footnote A.}
Another sentence.\footnote{Footnote B.}
Another sentence.\footnote{Footnote C.}
\end{document}

Answer 2

With package scrextend and \deffootnote you can use \addtokomafont or \setkomafont to change the font settings for the footnotemark:

\documentclass{book}

\usepackage{scrextend}
\setkomafont{footnotelabel}{\bfseries}
\deffootnote[.35in]{.5in}{.195in}{\makebox[.5in][r]{\thefootnotemark.\hspace{.1in}}}

\begin{document}
\noindent A sentence.\footnote{Footnote A.}
Another sentence.\footnote{Footnote B.}
Another sentence.\footnote{Footnote C.}
\end{document}

Using \addtokomafont or \setkomafont you can also change the font settings of the footnotemarks and the footnote text:

\documentclass{book}

\usepackage{scrextend}
\setkomafont{footnote}{\itshape}
\setkomafont{footnotelabel}{\bfseries}
\deffootnote[.35in]{.5in}{.195in}{\makebox[.5in][r]{\thefootnotemark.\hspace{.1in}}}

\begin{document}
\noindent A sentence.\footnote{Footnote A.}
Another sentence.\footnote{Footnote B.}
Another sentence.\footnote{Footnote C.}
\end{document}