catalina – How do I change an app icon image on the menu bar?

(macOS 10.15.7)

I want to change the icon image of an app on the menu bar, for example, the “syncing” image of Dropbox:

enter image description here

However, I cannot find the corresponding image in /Applications/ . Another post says changing the menu-bar icon may require the knowledge of Xcode.

Is it possible to change a menu-bar icon without using Xcode? Or is it possible to at least “shrink” the original icon (make it smaller but not disappear) without using Xcode?