Theory: Liquid Glass was originally supposed to “erase” text behind glass elements for legibility – but engineering ran out of time. Maybe this patent filed in 2017 is related: https://patents.google.com/patent/US20180350327A1/en – with its listed inventor no other than Bartosz Ciechanowski, a Core Animation engineer who you may know from his lovely blog https://ciechanow.ski
US20180350327A1 - Glyph-Mask Render Buffer - Google Patents

Systems, methods, and computer readable media to improve the operation of a computer's display system are described. In general, techniques are disclosed for retaining glyph-mask information for text associated with a region that may be arbitrarily moved across a screen. More particularly, techniques disclosed herein utilize an additional off-screen buffer referred to as the glyph-mask buffer. The glyph-mask buffer coincides with an existing side buffer in extent, but is used only to retain anti-aliased glyph information (i.e., glyph-masks). When the side buffer's content is updated, the effect of that update on the region's text may be reflected in an update to the glyph-mask buffer. At display time, the region corresponding to the side buffer, and the text therein, may be properly rendered at any screen location by combining the screen's target display area (background), the side buffer and the glyph-mask buffer.

@vlas I’m surprised they ran out of time when the Apple Maps top edge blur already erases the text labels
@Jon889 after digging a bit deeper into it, I suspect they were able to do it in Maps as a special, simpler case. Extending it to the general case would be more challenging.