It depends on the colors the dev chose for different elements of his theme.
Edit:
I am trying all the pre-installed themes and non of theme and non of them changes anything in thunar, The only thing that changes is the top bar of windows. I canāt understand what is supposed to change tbh.
Stop Thunar completely :
thunar -q
and then launch it again.
Itās not only Thunar, you should see the changes in the appearance window.
I think it maybe a bug. I look at picture of these themes and the coloring changes everywhere, Like in the window manager I choose the theme itself. But the only thing that changes for me is the blur in the main window and the title bar. look here as an example:
and this. Too totally different themes but everything looks the same
For the windows manager theme you have to check on the window of another application.
Like which application?
I used thunar and nothing happened.
It is working fine when I choose Arc-Dark instead of Arc-Darker in Appearance. Everything is now dark and comfy now. Thank you.
You should see the difference in Thunar or any application that is not an Xfce setting tool. 
edit: for the window manager (title bar and borders)
If I want to download an theme , I should add it to ~/.theme and it shows up in the menu? Or should I run a command too, manuals for it are confusing.
Thatās what I do when I use a theme that I canāt find in the official repo or in the AUR.
What is the name of these themes? I like the icons of the second one.
What should I search for in repos? Just search for theme?
The first is Fantome, a theme I found on Github few years ago, and Suru++ Aspromauros icon theme.
Second is Dracula with Flatery icon theme, my current desktop.
yay -S flatery-icon-theme-git
Search for āxfce themeā, āgtk themeā, āxfwm themeā and āicon themeā.
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Thanks