\documentclass{beamer}

\usetheme{Copenhagen}

\begin{document}

\begin{frame}
\begin{block}{}
Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut puruselit, vestibulum ut, placerat ac, adipiscing vitae, felis. Curabiturdictum gravida mauris. Nam arcu libero, nonummy eget, consectetuer id, vulputate a, magna. Donec vehicula augue euneque. Pellentesque habitant morbi tristique senectus et netus etmalesuada fames ac turpis egestas. Mauris ut leo. Cras viverrametus rhoncus sem. Nulla et lectus vestibulum urna fringillaultrices. Phasellus eu tellus sit amet tortor gravida placerat.Inte…

\documentclass{beamer}

\usetheme{Copenhagen}

\begin{document}

\begin{frame}
\begin{block}{}

\begin{enumerate}[<+->]
    \item

    \begin{itemize}
        \item In the 4th slide, it should not include the following item space:
        \begin{align*}
            a(x+1)^2-3x\uncover<+->{&=ax^2+2ax+a-3x=ax^2+x+1\\}
            \only<4>{&\implies ax^2+(2a-3)x+a=ax^2+x+1\\}
            \uncover<+->{&\implies\left\lbrace\begin{aligned}&a=a\\&2a-3=1\\&a=1\end{aligned}\right.}
        \end{align*}
        \item<only@5> More text here.

\beginonly % Starts from the last counted index, say 5
        \begin{enumerate}
            \item This starts from slide 5
            \item This starts from slide 6
            % ==== Whoops I forgot to add this! ====
            \item This is between 6 and 7:
            \begin{itemize}
                \item Text.
                \item Text.
            \end{itemize}
            % =======================================
            \item This starts from slide 7
        \end{enumerate}
    \endonly % Calculates all the indexes inside and returns the last counter index (which would be 10 …

\documentclass{beamer}

\usetheme{Copenhagen}

\begin{document}

\begin{frame}
\begin{block}{}

\begin{enumerate}[<+->]
    \item

    \begin{itemize}
        \item In the 4th slide, it should not include the following item space:
        \begin{align*}
            a(x+1)^2-3x\uncover<+->{&=ax^2+2ax+a-3x=ax^2+x+1\\}
            \only<4>{&\implies ax^2+(2a-3)x+a=ax^2+x+1\\}
            \uncover<+->{&\implies\left\lbrace\begin{aligned}&a=a\\&2a-3=1\\&a=1\end{aligned}\right.}
        \end{align*}
        \item<only@5> More text here.

\documentclass{article}
\usepackage{embrac}
\ExplSyntaxOn
\cs_set_protected:Npn \__embrac_replace:Nnnnn #1#2#3#4#5
  {
    \tl_replace_all:Nnn #1 {#3}
      {
        \mode_if_math:TF
          {#3} %<---instead of #4
          {
            \embrac_nobreak:
            \embrac_kern:n {#2}
            \embrac_nobreak:
            \embrac_braces_format:n {#3}
            \embrac_nobreak:
            \embrac_kern:n {#4}
            #5
          }
      }
  }
\ExplSyntaxOff
\begin{document}
\emph{$(d,d')$}

\documentclass[aspectratio=169]{beamer}
\usetheme{Copenhagen}
\usepackage{pgfplots}

\begin{document}

\begin{frame}

\begin{block}{}
\begin{columns}<.->[T]
    \begin{column}<.->{.5\linewidth}
        \begin{itemize}[<+->]
            \item $n=0$:

            \uncover<+->{\vspace{-.55cm}
                \begin{center}
                    \begin{tikzpicture}[scale=.45]
                        \begin{axis}[set layers=standard,clip=false]
                            \addplot {0};
                            \node<+-> (a) at (rel axis cs:-.5, .25) {$R_0$};

\documentclass[aspectratio=169]{beamer}
\usetheme{Copenhagen}
\usepackage{pgfplots}

\usetikzlibrary{overlay-beamer-styles}

\begin{document}

\begin{frame}

\begin{block}{}
\begin{columns}<.->[T]
    \begin{column}<.->{.5\linewidth}
        \begin{itemize}[<+->]
            \item $n=0$:

            \uncover<+->{\vspace{-.55cm}
                \begin{center}
                    \begin{tikzpicture}[scale=.45]
                        \begin{axis}[set layers=standard,clip=false]
                            \addplot {0};

> \AtBeginDocument=\long macro:
->\AddToHook {begindocument}.

\newif\ifprintout
\mode<handout>
  {
    \printouttrue
    \ifprintout
      % Version for handouts to print
      \definecolor{UEAorange}{RGB}{0,0,0}
      \setbeamertemplate{footline}[text line]{%
        \parbox{\linewidth}{\vspace*{-3em} \hfill \small \insertframestartpage}%
      }
      \AtBeginDocument{\let\alert\emph}
      \usepackage{pgfpages}
      \pgfpageslogicalpageoptions{1}{border code=\pgfstroke}
      \pgfpageslogicalpageoptions{2}{border code=\pgfstroke}
      \pgfpageslogicalpageoptions{3}{border code=\pgfstroke}