Appendix labels in table of content

I am using the book class and have several appendices. These are titled ‘Appendix A’, ‘Appendix B’, etc., where actually all letters are small caps. To achieve small caps for the labels (A, B, …), I use renewcommand{thechapter}{{normalfontscshape alph{chapter}}}. While that works fine, it also changes the appendix labels in the table of contents to small caps, which I don’t want. I can’t figure out how to avoid this. Does anyone know of a package, or a trick, that would make the labels A, B, etc., appear as normal capitals in the toc?

The following reproduces the problem:

documentclass[11pt,b5paper,twoside,dvipsnames]{book}
RequirePackage{luatex85}
usepackage{titlesec}
usepackage[top=1.2in,bottom=1.15in,right=1.15in,left=1.15in,headheight=50pt,headsep=4mm]{geometry}
usepackage[american]{babel}
usepackage[titletoc]{appendix}

addtocontents{toc}{protectsetcounter{tocdepth}{1}}

usepackage[no-math]{fontspec}
setmonofont[Scale=.753]{DejaVu Sans Mono}
usepackage{ebgaramond}
usepackage[cmintegrals,cmbraces]{newtxmath}
usepackage{ebgaramond-maths}
usepackage{anyfontsize}
usepackage[italic,defaultmathsizes,nolessnomore]{mathastext}
defaultfontfeatures{RawFeature={+calt,+clig,+dlig,liga,cv06}}

usepackage{fancyhdr}
pagestyle{fancy}
%setlength{headheight}{15pt}
renewcommand{chaptermark}[1]{markboth{#1}{}}
renewcommand{sectionmark}[1]{markright{thesection, #1}}
fancyhf{} % delete current setting for header and footer
fancyhead[LE,RO]{thepage}
fancyhead[CO]{textit{rightmark}}
fancyhead[CE]{leftmark}
renewcommand{headrulewidth}{0pt}
renewcommand{footrulewidth}{0pt}
addtolength{headheight}{50pt} % make space for the rule
fancypagestyle{plain}{%
fancyhead{} % get rid of headers on plain pages
renewcommand{headrulewidth}{0pt} % and the line
}

titleformat{chapter}[display]{}
    {filcenternormalfontromanspacedlargescshape chapter thechapter}
    {.2cm}
    {normalfontLargeromanspaceditshapefilcenter}
    
usepackage{titlesec}
titleformat{section}[block]{bfseriesfilcenter}{thesection}{1em}{}
titleformat{subsection}[block]{itshapefilcenter}{thesubsection}{1em}{}

begin{document}

author{Large Author}
date{}

frontmatter

title{Huge textsc{title} [5cm] {}}

maketitle

begingroup
defaultfontfeatures{Ligatures={NoContextual}}
setmainfont{EB Garamond}[
  Numbers={OldStyle,Monospaced},
]
fancyhead[C]{emph{Contents}}
tableofcontents
endgroup

pagestyle{fancy}

chapter{Preface}

fancyhead[CE]{leftmark}

Some text here ...

mainmatter

pagestyle{fancy}

fancyhead[CE]{leftmark}
fancyhead[CO]{textit{rightmark}}

chapter{Introduction}

Some more text ...

chapter{Second chapter}

... and more ...

appendix

renewcommand{thechapter}{{textsc{alph{chapter}}}}

titleformat{chapter}[display]{}
    {filcenternormalfontromanspacedlargescshape appendix thechapter}
    {.2cm}
    {normalfontLargeromanspaceditshapefilcenter}

appendixpage
noappendicestocpagenum
addappheadtotoc

chapter{Proof of Theorem 1}

... still more text ...

chapter{Proof of Theorem 2}

... and more ...

end{document}

{renewcommand{textsc}[1]{MakeUppercase #1}
tableofcontents
}