format of footer in appendices

Question

I'm using scrartcl document class with scrletter package in the preamble, for a letter with section capabilities. I want to add an appendices after my \end{letter} statement.

This is easy enough using appendix package, but the format of the footer is lost. In my letter I have formatted it per my answer here, but after making the \begin{appendices} ... environment, I get a single page number centered in the footer margin so the page style appears to have reset in the appendices environment.

How can I keep it consistent with the rest of my document/letter?

MWE:

\documentclass[a4paper,
headlines=8.1,
headheight=3cm,
%footlines=1.1,
%footheight=2cm,
parskip=full,
british]{scrartcl}

\usepackage[a4paper,
    %showframe,
rmargin=2cm,
marginparsep=0cm,
marginparwidth=0cm,
footskip=1cm,
lmargin=2cm,
bmargin=2cm,
tmargin=2cm]{geometry}

\usepackage[%
foldmarks=false,
fromalign=right,
fromrule=off,
refline=dateleft,
fromphone=false,
fromemail=true,
pagenumber=footright,
firstfoot=true,
fromlogo=false]{scrletter}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage[en-GB]{datetime2}
\DTMlangsetup[en-GB]{ord=raise}

\usepackage[british]{babel}
%\usepackage{showframe}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% dummy text
\usepackage{blindtext}
\usepackage{lipsum}

\usepackage[pdflang=en-GB]{hyperref}
\hypersetup{
    colorlinks=true,
    linkcolor=black,
    filecolor=magenta,
    urlcolor=blue,
    %pdftitle={Overleaf Example},
    %pdfpagemode=FullScreen,
}

\usepackage{appendix}

\setkomavar{firstfoot}{\thepage of \letterlastpage}
\renewcommand*\letterpagemark{\usekomafont{pagenumber}{\thepage of \letterlastpage}}

\setkomavar{myref}[Internal \#]{Testref1234}
\setkomavar{date}[Date]{\today}
\setkomavar{yourref}[Your \#]{Testref5678}
\setkomavar{fromname}{A N Other}
\setkomavar{signature}{A N Other}
\renewcommand*{\raggedsignature}{\raggedright}
\setkomavar{fromaddress}{%
    Building Number\\
    Street\\
    State\\
    ZIP Code%
}

\setkomavar{backaddress}{}
\setkomavar{subject}[]{\underline{Testing letter}}
\setkomavar{subjectseparator}[]{}

\begin{document}
    \begin{letter}{%
            A. Person\\
            Someplace\\
            ZIP CODE%
        }
        \opening{test}
        \lipsum[1-4]
        
        \blindtext
        
        \lipsum[1-4]\footnote{\blindtext}
        \closing{cheers}
    \end{letter}
\begin{appendices}
    %\pagestyle{plain}
    %\tableofcontents
    \appendixpageoff
    \appendixtitleoff
    \appendixheaderoff
    \appendixpagename
    
    % here I would put \section{} statements for each thing I want in the appendix
\end{appendices}
\end{document}

Answer 1

Use \appendix (without package appendix) inside the letter environment:

\documentclass[
  headheight=3cm,
  parskip=full,
  british
]{scrartcl}

\usepackage[
margin=2cm,
marginparsep=0cm,
marginparwidth=0cm,
footskip=1cm,
]{geometry}
%\usepackage{showframe}

\usepackage[%
  foldmarks=false,
  fromalign=right,
  fromrule=off,
  refline=dateleft,
  fromphone=false,
  fromemail=true,
  backaddress=false,
  subject=underlined,
  pagenumber=footright
]{scrletter}% <- loads package scrlayer-scrpage automatically

\usepackage[T1]{fontenc}
\usepackage[en-GB]{datetime2}
\DTMlangsetup[en-GB]{ord=raise}
\usepackage{babel}

\usepackage{lipsum}% dummy text

\usepackage[pdflang=en-GB]{hyperref}
\hypersetup{
  colorlinks=true,
  linkcolor=black,
  filecolor=magenta,
  urlcolor=blue
}

\renewcommand*\pagemark{\usekomafont{pagenumber}{\thepage\ of \letterlastpage}}% <- changed
\let\letterpagemark\pagemark% <- changed
\setkomavar{firstfoot}{\raggedleft\pagemark}% <- added

\setkomavar{myref}[Internal \#]{Testref1234}
\setkomavar{date}[Date]{\today}
\setkomavar{yourref}[Your \#]{Testref5678}
\setkomavar{fromname}{A N Other}
\setkomavar{signature}{A N Other}
\renewcommand*{\raggedsignature}{\raggedright}
\setkomavar{fromaddress}{Building Number\\Street\\State\\ZIP Code}
\setkomavar{subject}{Testing letter}

\begin{document}
\begin{letter}{A. Person\\Someplace\\ZIP CODE}
\opening{test}
\lipsum[1-9]\footnote{\lipsum[2]}
\closing{cheers}
\clearpage
\appendix% <- changed and moved in the letter environment
\tableofcontents
\section{An appendix section}
\lipsum
\section{Another appendix section}
\lipsum
\end{letter}
\end{document}

If \appendix should be outside letter environment, you can not use \letterlastpage, because it refers to the last page a letter inside the letter environment.

\documentclass[
  headheight=3cm,
  parskip=full,
  british
]{scrartcl}

\usepackage[
margin=2cm,
marginparsep=0cm,
marginparwidth=0cm,
footskip=1cm,
]{geometry}
%\usepackage{showframe}

\usepackage[%
  foldmarks=false,
  fromalign=right,
  fromrule=off,
  refline=dateleft,
  fromphone=false,
  fromemail=true,
  backaddress=false,
  subject=underlined,
  pagenumber=footright
]{scrletter}% <- loads package scrlayer-scrpage automatically

\usepackage[T1]{fontenc}
\usepackage[en-GB]{datetime2}
\DTMlangsetup[en-GB]{ord=raise}
\usepackage{babel}

\usepackage{lipsum}% dummy text

\usepackage[pdflang=en-GB]{hyperref}
\hypersetup{
  colorlinks=true,
  linkcolor=black,
  filecolor=magenta,
  urlcolor=blue
}

\renewcommand\pagemark{{\usekomafont{pagenumber}{\thepage\ of \pageref{LastPage}}}}% <- changed
\let\letterpagemark\pagemark
\AddToHook{shipout/lastpage}{\label{LastPage}}% <- added
\setkomavar{firstfoot}{\raggedleft\pagemark}

\setkomavar{myref}[Internal \#]{Testref1234}
\setkomavar{date}[Date]{\today}
\setkomavar{yourref}[Your \#]{Testref5678}
\setkomavar{fromname}{A N Other}
\setkomavar{signature}{A N Other}
\renewcommand*{\raggedsignature}{\raggedright}
\setkomavar{fromaddress}{Building Number\\Street\\State\\ZIP Code}
\setkomavar{subject}{Testing letter}

\begin{document}
\begin{letter}{A. Person\\Someplace\\ZIP CODE}
\opening{test}
\lipsum[1-9]\footnote{\lipsum[2]}
\closing{cheers}
\end{letter}
\appendix
\tableofcontents
\section{An appendix section}
\lipsum
\section{Another appendix section}
\lipsum
\end{document}