This is a modified version of nanodesu-xfwm4 by Loi Tran, from here: https://www.xfce-look.org/p/1242826/ (source: https://github.com/tdloi/nanodesu-xfwm4 )

It is a simple and pixel-perfect theme which improves the usability of the original nanodesu by removing the corner gaps while maximized to prevent clicking on nothing in the corner, increasing the click region size for resizing non-maximized windows from the corners, adapting to your GTK theme colors, and having different active, inactive, and button hover colors.

This theme is for window decorations only. You must use it alongside an overall theme. To do so, I personally use Xfce Theme Manager, which has an AUR package called xfce-theme-manager. There, you can choose nanodesu-nano in the "Window Borders" section.

To install:
Move zip file to "~/.themes" then extract it. There should be 4 directories: nanodesu, nanodesu-medium, nanodesu-large, and nanodesu-nano. The modified one described here is nanodesu-nano.
Use either Xfce Theme Manager or Window Manager to change your window border theme to this theme.

If you want the look that's in the attached screenshot, I personally use Matcha-dark-azul from 2021-11-29 (that date because newer versions make it less compact in Nemo, the file manager I use).