Using the package nicematrix you get the command \Block that serves both as multicolumn and multirow, also allowing the use of \\ inside.
So the code is more compact and is the only package needed to build the table.
Por example \Block{6-1}{Geo--Distributed \\ Load Balancing} creates a cell one column wide by six rows high, with two lines inside, text centered.
The table fits very well in a landscape orientation. (With the package pdflscape)
The result is very close to the example (please check the checks!).
Note that in the original table, the third row-second column cell is not aligned correctly.
This is the code.
\documentclass{article}
\usepackage{booktabs} % horizontal lines
\usepackage{nicematrix} % the table with NiceTabular
\usepackage{pdflscape} % landscape
\usepackage{amssymb} % checkmark
\usepackage{pdfrender}% bold checkmark
\newcommand*{\ck}{% https://tex.stackexchange.com/questions/383324/bold-checkmark
\textpdfrender{
TextRenderingMode=FillStroke,
LineWidth=1pt,
}{\Large\color{green!80!black}\checkmark}%
}
\begin{document}
\begin{landscape}
\thispagestyle{empty}
\begin{table}[htb!]
\centering
\caption{Research Summary}
\medskip
\label{tab:reseach}
\begin{NiceTabular}{@{}ccc ccc ccc@{}}[cell-space-limits = 4pt] % expand the cells vertically
\toprule
\Block{2-1}{Approach} & \Block{2-1}{Research Paper} & \Block{2-1}{Method} & \Block{1-3}{Power Supply} & & &\Block{1-3}{Optimization Objetives} \
\cmidrule(lr){4-6} \cmidrule(lr){7-9}
& & & Wind & Solar & \Block{}{Energy \ Storage} & Cost & \Block{}{RES \ Utilization} & Latency \
\midrule
\Block{3-1}{Power \ Managment} & Kwon [8] & Mathematical Optimizations &\ck & &\ck &\ck &\ck &\ck \
& I-Swithc [8] & Online Control Algorithm & & &\ck &\ck &\ck &\ck \
& Eco-Power [31]& Online Control Algorithm &\ck &\ck &\ck &\ck &\ck & \
\midrule
\Block{3-1}{Task Scheduling} & Greenslot [12]& Online Control Algorithm with Forecasting &\ck & & & &\ck &\ck \
& Lei [14] & Mathematical Optimization &\ck & & & &\ck &\ck \
& Qi [17] & Online Control Algorithm & & & &\ck & &\ck \
\midrule
\Block{6-1}{Geo--Distributed \ Load Balancing} & Buyya [11] & Forecasting ans Prediction &\ck &\ck & & & & \
& Aksanli [13] & Mathematical Optimization with Forecasting&\ck &\ck & &\ck &\ck &\ck \
& Toosi [18] & Machine Learning Algorithm &\ck &\ck & &\ck &\ck & \
& Xu [20] & Machine Learning Algorithm &\ck &\ck & &\ck & & \
& Zhou [19] & Machine Learning Algorithm & & & &\ck & &\ck \
& \Block{}{Proposed \ Algorithm} & Machine Learning Algorithm &\ck &\ck & &\ck &\ck &\ck \
\bottomrule
\end{NiceTabular}
\end{table}
\end{landscape}
\end{document}
It will compile twice the first time.
