Remove spaces between various elements

Question

I am trying to remove the space between the elements that I show in the following image. The space I talk about is denoted by the gray line (that line is not produced by LaTeX, it is merely a way to visualize the space in question)

To be more exact the spaces I want to reduce are:

1. Space between sections and subsections

2. Space between sections/subsections and text/images/math

3. Space between text images and math

How can I do that?

I have tried to use the followings but they didn't give me a good result and a good way to handle the spaces with precision.

\usepackage{titlesec}

\titlespacing\section{0pt}{12pt plus 4pt minus 2pt}{0pt plus 2pt minus 2pt}
\titlespacing\subsection{0pt}{12pt plus 4pt minus 2pt}{0pt plus 2pt minus 2pt}
\titlespacing\subsubsection{0pt}{12pt plus 4pt minus 2pt}{0pt plus 2pt minus 2pt}

\setlength{\abovedisplayskip}{0pt}
\setlength{\belowdisplayskip}{0pt}

MWE

\documentclass{article}

\usepackage
[   
    top = 0.2in,
    bottom = 0.2in,
    left = 0.2in,
    right = 0.2in,
]{geometry}

\usepackage[fontsize=8pt]{scrextend}

\usepackage{amsmath}

\usepackage{unicode-math}

\usepackage{parskip}

\setlength{\parindent}{0cm}

\usepackage{multicol}

\begin{document}

\setlength{\abovedisplayskip}{0pt}

\setlength{\belowdisplayskip}{0pt}

\columnseprule=0.8pt

\begin{multicols*}{4}

\section*{Section Title 1}

\subsection*{Subsection Title 1}

Text here

\subsection*{Subsection Title 2}
%
\begin{align*}
&x+y=1\\
&x+z=2
\end{align*}


\subsection*{Subsection Title 3}

\includegraphics[width=\columnwidth]{1.png}
%
\begin{equation*}
x+y=1
\end{equation*}

\includegraphics[width=\columnwidth]{2.png}

\subsection*{Subsection Title 4}

\includegraphics[width=\columnwidth]{1.png}
%
\begin{equation*}
x+y=1
\end{equation*}

\end{multicols*}


\end{document}