This mod has been on my list for a while. I think the default spacing is just huge.
Back in Windows XP, there were 2 pixels between each tray icon. It was increased to 8 in Windows 7, and then to 16 in newer Windows 11 versions. I think that 8 is fine but 16 is just too much for a desktop computer.
You can get the Taskbar notification icon spacing mod here.
Enjoy, and let me know if you encounter any problems.