\usepackage[
  backend=biber,
  style=ext-alphabetic,
  backref=true,% Show page numbers where citations appear
  maxbibnames=99,% Show all authors in bibliography
  maxalphanames=1,% Show only one author in citations keys
  maxcitenames=1,% Show only one authors in citations in text
  uniquelist=false% Force to show only one author in citations
]{biblatex}

% Define citation style to be [Author, Year]
% From https://tex.stackexchange.com/a/176119
\DeclareLabelalphaTemplate{%
  \labelelement{% Author
    \field[final]{shorthand}%
    \field{labelname}%
    \field{label}%
  }%
  \labelelement{% Comma
    \literal{,\addhighpenspace}%
  }%
  \labelelement{% Year
    \field{year}%
  }%
}

% Use prefix + family name for 'Author' in citation keys
\DeclareLabelalphaNameTemplate{%
  \namepart[use]{prefix}%
  \namepart{family}%
}

\renewcommand*{\labelalphaothers}{\ et~al.}% Use "et al." in citation keys

% Define \textcite to be Author [Yeara] (magically defined by Copilot)
\DeclareCiteCommand{\textcite}
{\usebibmacro{prenote}}
{%
  \ifciteindex{\indexnames{labelname}}{}%
  \bibhyperref{\printnames{labelname}}% Author
  \setunit{\addspace}% Space
  \printtext[brackets]{\bibhyperref{\printdateextra}}% Year
}
{\multicitedelim}
{\usebibmacro{postnote}}

% Remove some fields from bibliography
\AtEveryBibitem{
  \ifentrytype{book}{}{% Keep ISBN only for books
    \clearfield{isbn}%
  }%
  \clearfield{day}%
  \clearfield{doi}%
  \clearlist{editor}%
  \clearfield{extra}%
  \clearfield{location}%
  \clearfield{month}%
  \clearfield{series}%
  \clearlist{publisher}%
  \clearfield{url}%
}

% References section (https://tex.stackexchange.com/a/298992)
% tex-fmt: off
\setlength{\biblabelsep}{2\labelsep}%
\defbibenvironment{bibliography}{%
  \list{%
    \printtext[labelalphawidth]{%
      \printfield{prefixnumber}%
      \printfield{labelalpha}%
      \printfield{extraalpha}%
    }%
  }{%
    \setlength{\labelsep}{\biblabelsep}%
    \setlength{\leftmargin}{\labelsep}%
    \setlength{\itemsep}{\bibitemsep}%
    \setlength{\parsep}{\bibparsep}%
  }%
\renewcommand*{\makelabel}[1]{##1\hss}%
}{\endlist}%
{\item}%
% tex-fmt: on