将信息放在第一页底部时出现问题

Question

您需要更改\textheight第一页的。要自动调整，如果页脚的高度可能会改变，请使用框

\newbox\firstfootbox
\sbox{\firstfootbox}{%
  \parbox[t]{\textwidth}{%
    \rule{3cm}{0.5pt}
    \footnotesize
    \vskip1.5pt
    \@corres\par
    \@doi\par
    \@footinfo\par
  }%
}

页脚的额外高度与框深度相对应（使用[t]，\parbox顶线与基线对齐）。从\textheight

\addtolength{\textheight}{-\dp\firstfootbox}

并在页脚中调用框内容

\fancyfoot[L]{\usebox{\firstfootbox}}

最后，你需要恢复下一页的几何形状。你可以用钩子来做

\AddToHookNext{shipout/after}{
  \restoregeometry
  \global\textheight=\textheight
}

由于长度分配是本地的，因此\global\textheight=\textheight是需要的（它是唯一被改变的长度\restoregeometry）。

我建议创建一个包含所有几何设置的命令

\NewDocumentCommand{\firstpagegeometry}{}{%
  \sbox{\firstfootbox}{%
    \parbox[t]{\textwidth}{%
      \rule{3cm}{0.5pt}
      \footnotesize
      \vskip1.5pt
      \@corres\par
      \@doi\par
      \@footinfo\par
    }%
  }
  \addtolength{\textheight}{-\dp\firstfootbox}
  \AddToHookNext{shipout/after}{
    \restoregeometry
    \global\textheight=\textheight
  }
}

并在之前调用它\maketitle。

完整示例：

\begin{filecontents*}{example.cls}
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{example}[2024/03/28 Rho LaTeX class]
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{extarticle}}
\ProcessOptions\relax
\LoadClass[twocolumn]{extarticle}
\AtEndOfClass{\RequirePackage{microtype}}

% ---------------------------------------------

\usepackage[utf8]{inputenc}
\usepackage{lipsum}
\usepackage{stix2}
\usepackage{fancyhdr}
\usepackage{xifthen}
\usepackage{etoolbox}
\usepackage{algorithm}
\usepackage{adjustbox}
\usepackage{iflang}
\usepackage{ragged2e}
\usepackage{url}

% ---------------------------------------------

\usepackage[left=1.25cm, right=1.25cm, top=2cm, bottom=2cm, headsep=0.75cm]{geometry}

% ---------------------------------------------

\newcommand\correspondingauthor[2][]{
  \gdef\@corres{\textsuperscript{#1}\fontsize{6.5}{9}\selectfont#2}
}
\newcommand{\footerfont}{\normalfont\fontsize{7}{9}\selectfont}
\newcommand{\institution}[1]{\def\@institution{#1}}
\newcommand{\etal}[1]{\def\@etal{#1}}
\newcommand{\course}[1]{\def\@course{#1}}
\newcommand{\doi}[1]{\def\@doi{#1}}
\newcommand{\footitle}[1]{\def\@footitle{#1}}
\newcommand{\footinfo}[1]{\def\@footinfo{#1}}

% ---------------------------------------------

\pagestyle{fancy}

\newbox\firstfootbox

\NewDocumentCommand{\firstpagegeometry}{}{%
  \sbox{\firstfootbox}{%
    \parbox[t]{\textwidth}{%
      \rule{3cm}{0.5pt}
      \footnotesize
      \vskip1.5pt
      \@corres\par
      \@doi\par
      \@footinfo\par
    }%
  }
  \addtolength{\textheight}{-\dp\firstfootbox}
  \AddToHookNext{shipout/after}{
    \restoregeometry
    \global\textheight=\textheight
  }
}

\fancypagestyle{firststyle}{
  \fancyhead[R]{}
  \fancyhead[L]{}
  \fancyfoot[R]{}
  \fancyfoot[L]{\usebox{\firstfootbox}}
}

  % Header
\fancyhead[C]{}
\fancyhead[RE]{\sffamily\footnotesize{\itshape\@title}\hspace{10pt}{\bfseries\thepage}}
\fancyhead[LO]{\sffamily\footnotesize{\bfseries\thepage}\hspace{10pt}{\itshape\@title}}
\fancyhead[LE]{}
\fancyhead[RO]{}

% Footer
\lfoot{}%
\cfoot{}%
\rfoot{}%

\fancyfoot[RO]{\sffamily\footnotesize\@institution\hspace{10pt}{\bfseries\@date}\hspace{10pt}\@footitle}
\fancyfoot[LO]{\sffamily\footnotesize\@etal}
\fancyfoot[RE]{\sffamily\footnotesize\@etal}
\fancyfoot[LE]{\sffamily\footnotesize\@course}

\renewcommand{\headrulewidth}{0pt} % No header rule
\renewcommand{\footrulewidth}{0pt} % No footer rule
\end{filecontents*}

\documentclass[9pt,a4paper,twoside]{example}

% ---------------------------------------------

\title{Example}
\author{Author 1}
\date{April 2024}

% ---------------------------------------------
% Using the commands
% ---------------------------------------------

\correspondingauthor[$\ast$]{Corresponding author at: This is an example of how
  you can customize this part of the article. Please, provide the corresponding
  author information and publisher here. \textit{E-mail address:}
  [email protected].}

\footinfo{Available Online \\ Available date. XXXX-XX/ \copyright\ All
  rights reserved.}

\doi{\url{https://www.doi.org/exampledoi/XXXXXXXXXX}}

\institution{Example}

\etal{Author last name et al.}

\footitle{Example}

\course{Example}

%---------------------------------------------

\begin{document}

\firstpagegeometry

\maketitle
\thispagestyle{firststyle}

\lipsum[2-10]
\\

\textbf{On the first page the footer is different from the rest of the pages.
  I would like to implement something that always shows below but automatically
  adjusts to the lines that are placed in case I have more information.}\\

\textbf{As I placed it now, you can see that the bottom margin is smaller than
  the top one and I would like them to be the same.}

\newpage

\textbf{Here the footer change. But if you tried to make the footer larger to
  fit the information for the first page, it no longer looks good because it
  looks unnaturally large on the other pages.}

\lipsum[2-10]

\end{document}

Answer 1