possible to enable "gumdrop" buttons (close/minimize/zoom) in all windows (disable auto-hide of these buttons for non active window)?
No, what you're asking for is not possible.  There's no &quot;tweak&quot; to remove the &quot;auto hide feature&quot; because it's not a feature; it's a design element of macOS.
Apple provides very specific guidance when working with the Title Bar within the Frame in their guidelines in Window Anatomy of their Human Interface Guidelines for macOS:


This is how users interact with the system and specifically, this is how they know what window is active or not.  Apple goes out of their way to document how users should interact with every element; their not going to supply a way to circumvent it.  For context, this can't be done in any OS GUI that I can think of ranging from Windows to GNOME, KDE, XFCE, etc.  There's no reason for Apple to deviate from this standard.