For pure transparency, sure, but most of the liquid glass effects aren't pure transparency and there's a lot of different ways you can modulate the effect. Perhaps the simplest example of something like this is the mouse cursor. You probably don't think about it, but that cursor in macos has a thin white single pixel border around the whole cursor. On light backgrounds, it effectively disappears, but on dark and black backgrounds it allows you to easily see and follow your cursor around the screen. The cursor itself isn't changing, but the chosen design allows a single "black" cursor to work across all backgrounds.

Or the menu bar which has had a transparency effect for a version or two now auto switches between black and white text depending on the background coloring (for what its worth, so does Safari's new control bar). But in neither of these cases (the mouse or the menu bar) is the UI changing dramatically. Unlike the safari controls, when the mouse pointer loses its border, it doesn't lose depth or become harder to make out. When the text in the menu bar changes color, it doesn't switch from "popping out" to "flat on the bar". The style and overall look remains the same even as the colors adjust for the environment.

What I'm saying is that Apple needs to spend some time shoring up those sort of little touches that can and do make the UI fee thought out instead of just slapped together.

I suspect that you have got it in one, here.