Animating the Liquid Glass widgets does seem to cost something / produce lag. But I get the impression that this is down to the UI toolkit not being optimized for whatever Liquid Glass is doing in terms of recalculating constraints during animations. (When the GPU stutters, you get dropped frames, not lag. Lag is the CPU stuttering.)

I get the sense that Apple rushed out some shitty code that has some of these components re-evaluating a bunch of their placement and sizing constraints on every non-static animation frame (rather than just giving the Liquid Glass shaders the ability to do declarative tweens.)

Or maybe the shaders already do declarative tweens, but they are doing the redundant on-CPU per-frame recalculations, to re-do any constraint-based layout for everything around the component during the animation, that might be impacted by the component's tween. I dunno. (Either way, silly; the shader can just spit numbers out into a VRAM buffer that gets transferred to the CPU on each frame.)