Here is a suggestion based on assumptions and gesses about the documentclass and citations used. I have used a left aligned p type column for the first column as well as for the last column. To get the bullet points in the last column, I have defined a new environment tabitem with the help of the enumitem package. Lastly, I have removed teh nested tabulars in columns 2-4 and used left aligned X txpe columns for them.
As you can see from the following screenshots and example, you could even increase teh font size from \scriptsize fo \footnotesize of even \small and still fit the table nicely into the textwidth. If your table should becoome too long for a single page, you might want to have a look at the xltabular package.

\documentclass{article}
\usepackage{geometry}
\usepackage{tabularx}
\usepackage{tabulary}
\usepackage{booktabs}
\usepackage{enumitem}
\newlist{tabitem}{itemize}{1}
\setlist[tabitem]{wide=0pt, nosep, leftmargin= * ,label=\textbullet,after=\vspace{-\baselineskip},before=\vspace{-0.6\baselineskip}}
\usepackage[style=authoryear-comp]{biblatex}
\addbibresource{\jobname.bib}
\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@book{ma2017designing,
author = {Ma, A.},
year = {2007},
title = {Title},
publisher = {Publisher},
}
@book{hyland2018dynamic,
author = {Hyland, A. and Mahmassani},
year = {2018},
title = {Title},
publisher = {Publisher},
}
\end{filecontents}
\begin{document}
\begin{table*}[th!]
\center
\scriptsize
\caption{Systematic literature review.\label{tab:lit_rev}}
\begin{tabularx}{\textwidth}{>{\raggedright\arraybackslash}p{1.5cm}*{3}{>{\raggedright\arraybackslash}X}lp{4cm}}
Article & Methodology & Model\newline objective & Decision phase & Vehicle Types & Features\\
\toprule
\cite{ma2017designing} & Linear programming & Minimize traffic on arcs & Operational, rolling horizon & SAV & \begin{tabitem} \item No carpooling \item Parking at any node \item Simulated traffic congestion \item Flexible departure times\end{tabitem} \\
\midrule
\cite{hyland2018dynamic} & Agent-based simulation & Minimize miles driven and client wait times & Operational, rolling horizon, real-time & SAV & \begin{tabitem}\item No carpooling \item No info on parking \item No traffic congestion \item Flexible pick up time \item Fixed number of AVs per day\end{tabitem} \\
\bottomrule
\end{tabularx}
\end{table*}
\begin{table*}[th!]
\center
\footnotesize
\caption{Systematic literature review.\label{tab:lit_rev}}
\begin{tabularx}{\textwidth}{>{\raggedright\arraybackslash}p{1.5cm}*{3}{>{\raggedright\arraybackslash}X}lp{4.2cm}}
Article & Methodology & Model\newline objective & Decision phase & Vehicle Types & Features\\
\toprule
\cite{ma2017designing} & Linear programming & Minimize traffic on arcs & Operational, rolling horizon & SAV & \begin{tabitem} \item No carpooling \item Parking at any node \item Simulated traffic congestion \item Flexible departure times\end{tabitem} \\
\midrule
\cite{hyland2018dynamic} & Agent-based simulation & Minimize miles driven and client wait times & Operational, rolling horizon, real-time & SAV & \begin{tabitem}\item No carpooling \item No info on parking \item No traffic congestion \item Flexible pick up time \item Fixed number of AVs per day\end{tabitem} \\
\bottomrule
\end{tabularx}
\end{table*}
\begin{table*}[th!]
\center
\small \setlength{\tabcolsep}{4pt}
\caption{Systematic literature review.\label{tab:lit_rev}}
\begin{tabularx}{\textwidth}{>{\raggedright\arraybackslash}p{2cm}*{3}{>{\raggedright\arraybackslash}X}lp{4.4cm}}
Article & Methodology & Model\newline objective & Decision phase & Vehicle Types & Features\\
\toprule
\cite{ma2017designing} & Linear programming & Minimize traffic on arcs & Operational, rolling horizon & SAV & \begin{tabitem} \item No carpooling \item Parking at any node \item Simulated traffic congestion \item Flexible departure times\end{tabitem} \\
\midrule
\cite{hyland2018dynamic} & Agent-based simulation & Minimize miles driven and client wait times & Operational, rolling horizon, real-time & SAV & \begin{tabitem}\item No carpooling \item No info on parking \item No traffic congestion \item Flexible pick up time \item Fixed number of AVs per day\end{tabitem} \\
\bottomrule
\end{tabularx}
\end{table*}
\end{document}