alaligne not working on tikzpicture environment

Maybe with splitting your music environment in two (start)pieces you can add the comments you want, taking into account that you know where you want to insert the line breaks:

\documentclass[%
border={35pt 100pt 150pt 5pt},% left bottom right top
varwidth]{standalone}

% ========== PAQUETES ==========
\usepackage{tikz}
\usetikzlibrary{arrows.meta,calc} %LIBRERIA PARA LAS FORMAS
\usetikzlibrary{quotes}
\usetikzlibrary{shapes}
\usetikzlibrary{fit,positioning}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{decorations}
\usepackage{amsmath}%
\usepackage{musicography}%
\usepackage{musixtex}%
\input musixlyr%
\usepackage{xcolor}%
\xdefinecolor{red-undar}{RGB}{179,35,79}

\begin{document}%
%\begin{tikzpicture}
%\node[anchor=north west, inner sep=0pt] (score) at (0,0) {%
\begin{music}%
\resetlyrics%
\font\A=phvb8t at 10pt%
\font\B=phvb8t at 8pt%
\setsongraise1{-1.5mm}%
\staffbotmarg3\Interligne%
\setclef1\treble%
\nobarnumbers%
\nostartrule%   
%\startextract%
\begin{tikzpicture}%
\node[anchor=north west, inner sep=0pt] (score) at (0,0) {%
\startpiece%\addspace\afterruleskip%
% AQUI EMPIEZOOO
\Notes\zw{h}\hu{j}\qsk\hu{l}\en\bar%
\Notes\zw{f}\hu{k}\qsk\hu{j}\en\bar%
\Notes\zw{g}\hu{i}\sk\en\setdoublebar\bar%
\Notes\zw{h}\hu{m}\qsk\hu{l}\en\bar%
\Notes\zw{f}\hu{k}\qsk\hu{j}\en\bar\setdoublebar%
\Notes\zw{g}\hu{i}\sk\en%\alaligne%%
\setdoublebar\endpiece%
};\end{tikzpicture}%

\bigskip%
\begin{tikzpicture}%
\node[anchor=north west, inner sep=0pt] (score) at (0,0) {%
\startpiece%
\Notes\zw{b}\hu{g}\qsk\hu{f}\en\bar%
\Notes\zw{c}\hu{e}\qsk\hu{g}\en\setdoublebar\bar%
\Notes\zw{g}\hu{i}\qsk\hu{k}\en\bar%
\Notes\zw{c}\hu{l}\qsk\hu{n}\en\setdoublebar%
\endpiece%
};\end{tikzpicture}%
%\endextract%
\end{music}%
%};
% CURVA 1
%   \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(-1.1cm,-0.7cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(-1.7cm,-1.2cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(-1.9cm,-1.0cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(-2.0cm,-1.1cm)$);   % punto FIN (nota abajo)
%       
%       % CURVA 2
%       \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(0.6cm,-0.9cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(0.5cm,-1.1cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(0.2cm,-1.2cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(-0.1cm,-1.2cm)$);   % punto FIN (nota abajo)
%       
%       % CURVA 3
%       \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(4.1cm,-0.7cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(3.8cm,-1.0cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(3.6cm,-1.0cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(3.2cm,-1.1cm)$);   % punto FIN (nota abajo)
%       
%       % CURVA 4
%       \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(5.8cm,-0.9cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(5.6cm,-1.1cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(5.4cm,-1.2cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(5.1cm,-1.2cm)$);   % punto FIN (nota abajo)
%       
%       % CURVA 5
%       \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(9.2cm,-1.3cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(9.1cm,-1.5cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(8.7cm,-1.6cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(8.4cm,-1.6cm)$);   % punto FIN (nota abajo)
%       
%       % CURVA 6
%       \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(11.0cm,-1.2cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(10.8cm,-1.4cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(10.5cm,-1.5cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(10.2cm,-1.5cm)$);   % punto FIN (nota abajo)
%       
%       % CURVA 7
%       \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(12.9cm,-0.8cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(12.8cm,-1.0cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(12.4cm,-1.2cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(12.0cm,-1.2cm)$);   % punto FIN (nota abajo)
%       
%       % CURVA 8
%       \draw[line width=0.9pt, color=red-undar]
%       ($(score.north west)+(14.6cm,-0.6cm)$)    % punto INICIO (nota arriba)
%       .. controls
%       ($(score.north west)+(14.5cm,-1.1cm)$)    % punto control 1 (curva izquierda)
%       and
%       ($(score.north west)+(14.2cm,-1.4cm)$)    % punto control 2 (curva izquierda)
%       ..
%       ($(score.north west)+(13.9cm,-1.5cm)$);   % punto FIN (nota abajo)
%       
%       \node[anchor=south west] at ($(score.north west)+(1.6cm, -0.6cm)$)
%       {\small\textbf{Etc.}};
%       
%       \node[anchor=south west] at ($(score.north west)+(6.9cm, -0.6cm)$)
%       {\small\textbf{Etc.}};
%       
%       \node[anchor=south west] at ($(score.north west)+(0.0cm, -0.2cm)$)
%       {\small\textbf{a)}};
%       
%       \node[anchor=south west] at ($(score.north west)+(5.1cm, -0.2cm)$)
%       {\small\textbf{b)}};
%       \\
%       \node[anchor=south west] at ($(score.north west)+(9.5cm, -0.2cm)$)
%       {\small\textbf{c)}};
%       \node[anchor=south west] at ($(score.north west)+(13.1cm, -0.2cm)$)
%       {\small\textbf{d)}};
% PUNTOS DE REFERENCIA
%\fill[red]   ($(score.north west)+(4.4cm,-0.9cm)$) circle (1pt); % INICIO
%\fill[blue]  ($(score.north west)+(0.5cm,-1.2cm)$) circle (1pt); % FIN
%\fill[green] ($(score.north west)+(14.5cm,-0.9cm)$) circle (1pt); % CONTROL 1
%\fill[green] ($(score.north west)+(14.2cm,-1.1cm)$) circle (1pt); % CONTROL 2
%\end{tikzpicture}
\end{document}%

\bigskip is my old fashioned way to have a larger line break within music. You can see where I disactivated the \begin{tikzpicture} etc. and where I inserted it.