Classic Mac OS window headers had striped or dot patterns that were kind of similar to rugged parts of various physical tool handles. So they were both decorative in a way and informational: this is a part you can hold and drag around. A typical interface will have a lot of such parts that are both functional and decorative, so it will feel just right.
Purely decorative parts are also possible (and even desirable), but they should be personal. A set of colors chosen by the user, a background texture, a picture that the user keeps on the desktop and so on.
Everything in a UI needs to not hinder usefulness. Adding more information signals (icons) which don't actually convey meaning is clutter that makes the UI harder to parse. That factor is far more important than whether it feels "alive".
Menus should not feel alive. Because they are menus, at any given point they mostly contain things the user does not want to interact with right now. Menu icons that serve as visual anchors are good, they help the task of finding the desired action, as well as building a visual memory. Icons everywhere achieve the opposite, for the spurious benefit of visual consistency. Menu items are not consistent affordances, they perform very different actions that are at best related, but oftentimes they are there because they need to be somewhere.
You remind me of my favourite bit of Windows software ever[0]. It made the desktop feel really alive with things like can-can girls and humanoid fish flying around your "living wallpaper".
Then again it was named Monty Python's Complete Waste of Time, so maybe it's not such a good idea for the default environment of a general-purpose operating system.
A decorative element can be fine in a design model, but 1) a good design tends to have no purely decorative elements, and 2) it becomes problematic when the decorative element looks like a meaningful element but does not actually carry meaning (or the intended meaning).
We all recognise an icon in a menu as a meaningful element. Treating it as a decorative element is wrong and adds mental overhead, as we tend to scan every one of those icons (putting it at the beginning of menu text, i.e., to the left for LTR languages, makes it worse). It is well-known we do tend to scan these icons because that is the reason icons work: repeated exposure creates intuition. If this intuition is not put to use, then all such icons are a waste of our attention.
For example, a bullet in a list: fine (differentiates where each list item starts), window shadow or the 3D effect on window close buttons: fine (meaningful in terms if differentiating areas in the GUI, not pretending to do more); whitespace to set apart one thing more from another thing than from the third thing: fine (if that reflects the relationship between those things).
... until the not-useful becomes distracting and/or causes information overload.
In the case of Apple, I've been a user of the Accessibility menu ever since they introduced the stupid parallax wiggling of the icons. Right now i use: reduce motion, bold text and reduce transparency. Because I want to see what I'm looking for when using the phone and not squint through pointless effects.
Or keep it since decoration makes interfaces feel more alive.
Not everything NEEDS to be useful