Horizontal and vertical braces below and next to a tabular table

Question

I need to reproduce some stuff made in Power Point to Latex beamer. Some of the slides contain braces and text bubbles in various sizes and arrangements. Since I'm new to this whole Latex thing I probably just butchered it in somehow so far (sorry for that). I just would really like to get to know a way to arrange these braces and textbubbles in a better way than to position them with tikz manually, since this is something I have to do multiple times. Also, I can't find a way to get the vertical braces to work in a similar way than in the example. Would be very thankful for some help.

Edit: I really like the idea of putting a \tikzmark{} somewhere and use it as anchor points.

Desired outcome:

My approach so far which I mostly copied from some similar question (without colors and stuff to keep it slim):

\documentclass[presentation, aspectratio=1610, 12pt, t]{beamer}
\usepackage{tikz} 
\usetikzlibrary{cd,arrows, decorations.markings, backgrounds, shapes.multipart,matrix,positioning, shapes, fit,decorations.pathreplacing,angles,quotes,decorations.pathreplacing,calc}

\usepackage{multirow} %adds the possibility to create columns spanning mulitple rows

\newcommand{\tikzmark}[1]{\tikz[overlay,remember picture] \node (#1) {};}
\newcommand*{\BraceAmplitude}{0.5em}%  Can be tweaked if
\newcommand*{\VerticalOffset}{1.2ex}%  necessary.
\newcommand*{\HorizontalOffset}{0.8ex}%  necessary.
\newcommand*{\InsertUnderBrace}[4][]{%
    \begin{tikzpicture}[overlay,remember picture]
\draw [decoration={brace,amplitude=\BraceAmplitude},decorate, thick,draw=black,text=black,#1]
        ($(#3)+(\HorizontalOffset,-\VerticalOffset)$) -- 
        ($(#2)+(-\HorizontalOffset,-\VerticalOffset)$)
        node [below=\VerticalOffset, midway] {#4};
    \end{tikzpicture}%
}%

\begin{document}
\begin{frame}
\begin{tabular}{l l l l l l | l}
    1 & 2 & 3 & 4 & 5 & 6 & 7 \\ \hline
    A & test & 2 & U & 14 & A & \\ 
    A & test & 2 & U & 14 & A & \multirow{ -2}{*}{L1} \\ 
    A & test & 2 & U & 14 & A & \\
    A & test & 2 & U & 14 & A &  \\
    A & test & 2 & U & 14 & A &  \\
    A & test & 2 & U & 14 & A &  \multirow{ -4}{*}{L2} \\
    \tikzmark{start1}...&...&...&...&...&...{ }\tikzmark{end1}&\tikzmark{start2}... \tikzmark{end2}\\
\end{tabular}
\normalsize

\InsertUnderBrace[draw=black,text=black]{start1}{end1}{Pretty loooong text here
}
\InsertUnderBrace[draw=black,text=black]{start2}{end2}{Explanation}

\tikz\draw [remember picture,overlay,thick, black,decorate,decoration={brace,amplitude=10pt,mirror},xshift=0pt,yshift=0pt](3,-1) -- (8,-1) node[black,midway,yshift=-0.6cm] {\footnotesize $Made with tikz$};
\end{frame}
\end{document}

Answer 1

a little bit more sophisticated, as tikz picture:

\documentclass[presentation, aspectratio=1610, 12pt, t]{beamer}
\usepackage{tikz}
\usetikzlibrary{arrows,
                calc,
                decorations.pathreplacing,
                calligraphy,% had to be after decorations.pathreplacing
                matrix,
                positioning
                }

\begin{document}
\begin{frame}[fragile]
\[
    \begin{tikzpicture}[
node distance = 0pt,
    BC/.style = {
        decorate,
        decoration={calligraphic brace, amplitude=1.2mm,
        pre =moveto, pre  length=0.75pt,
        post=moveto, post length=0.75pt,
        raise=1mm,
        #1},% for mirroring of brace
        very thick,
        pen colour={red}% black ...
                  },
  BC/.default = mirror,
    LN/.style = {inner xsep=4pt, outer sep=0pt},
                        ]
\matrix (m) [matrix of nodes, inner sep=0pt,
             nodes={text depth=0.8ex, text height=1em, %minimum width=5ex,
                    inner ysep=1pt, inner xsep=4pt, outer sep=0pt, anchor=west},
             nodes in empty cells,
             column sep=-\pgflinewidth,
             row sep= -\pgflinewidth,
             ]
{
    1   & 2     & 3     & 4     & 5     & 6     & 7     \\
    A   & test  & 2     & U     & 14    & A     &       \\
    A   & test  & 2     & U     & 14    & A     &       \\
    A   & test  & 2     & U     & 14    & A     &       \\
    A   & test  & 2     & U     & 14    & A     &       \\
    A   & test  & 2     & U     & 14    & A     &       \\
    A   & test  & 2     & U     & 14    & A     &       \\
\dots   & \dots & \dots & \dots & \dots & \dots & \dots \\
};
\node[LN,right=of m-2-6.south -| m-1-7.west] {L1};
\node[LN,right=of m-5-6.south -| m-1-7.west] {L2};
\draw           (m-1-1.south west) -- (m-1-7.south east);
\draw[BC={}]    (m-2-7.north -| m.east) --
                    node[right=3mm] {bla bla 1}
                (m-3-7.south -| m.east);
\draw[BC={}]    (m-4-7.north -| m.east) --
                    node[right=3mm] {bla bla 2}
                (m-7-7.south -| m.east);
%
\draw[BC]   let \p1 = ($(m-1-1.west)-(m-1-6.east)$),
                \n1 = {veclen(\x1,\y1)} in
            (m-8-1.south west) --
                node[text width=\n1, align=center,
                     below=3mm] {Pretty loooong loooong loooong loooong loooong loooong loooong loooong text here}
            (m-8-6.south east)
                    ;
\draw[BC]   (m-8-7.south west) --
                node[align=center, below=3mm] {Expla- \\
                                               nation}
            (m-8-7.south east);
    \end{tikzpicture}
\]
\end{frame}
\end{document}

Answer 2

A simple answer (quickly tested) : use a minipage !

\InsertUnderBrace[draw=black,text=black]{start1}{end1}{\begin{minipage}{3cm}Pretty loooong text here\end{minipage}}
\InsertUnderBrace[draw=black,text=black]{start2}{end2}{Explanation}