It is not clear, where should be vertical positioned image. If you like to have in the vertical middle of cells, than see the following solution:
\documentclass{article}
\usepackage{graphicx}
\usepackage{array, longtable}
\usepackage{enumitem}
\usepackage{etoolbox}
\AtBeginEnvironment{longtable}{%
\setlist[itemize]{nosep,
leftmargin=*,
label=\textbullet,
before={\begin{minipage}[t]{\hsize}},%https://tex.stackexchange.com/questions/531952/
after ={\end{minipage}}
} }
\begin{document}
\begin{longtable}{ | m{0.3\linewidth} | m{3cm} | }
\hline
Graph & Items \
\hline
\includegraphics[width=\linewidth]{example-image-duck}
& \begin{itemize}
\item Item 1
\item Item 2
\item Item 3
\item Item 4
\item Item 5
\item Item 6
\item Item 7
\item Item 8
\item Item 9
\item Item 10
\end{itemize} \
\hline
\end{longtable}
\end{document}

In the case, that you like to have at top of cell, than try the following:
\documentclass{article}
\usepackage[export]{adjustbox} % it load graphicx too
\usepackage{array, longtable}
\usepackage{enumitem}
\usepackage{etoolbox}
\AtBeginEnvironment{longtable}{%
\setlist[itemize]{nosep,%
leftmargin=*,
label=\textbullet,
before={\begin{minipage}[t]{\hsize}},%https://tex.stackexchange.com/questions/531952/
after ={\end{minipage}}
} }
\begin{document}
\begin{longtable}{ | p{0.3\linewidth} | p{3cm} | }
\hline
Graph & Items \
\hline
\includegraphics[width=\linewidth, valign=t, margin=2pt]{example-image-duck}
& \begin{itemize}
\item Item 1
\item Item 2
\item Item 3
\item Item 4
\item Item 5
\item Item 6
\item Item 7
\item Item 8
\item Item 9
\item Item 10
\end{itemize} \
\hline
\end{longtable}
\end{document}

width=.2\textwidthor whatever you need, you can control the vertical alignment with\raiseboxor using valign key added by adjustbox package. – David Carlisle Jul 06 '21 at 13:06