macOS 26 Liquid Glass effects not correctly displayed due to SDK

[freakboy3742]

Bug report

Bug description:

macOS 26 has introduced a bunch of new styling features, collectively referred to as "Liquid Glass".

Historically, the appearance of widgets on macOS has been determined by the version of the operating system that is running the app; however, it appears that some features of Liquid Glass are not enabled unless the app itself has been compiled against a macOS 26 SDK.

Since python.exe is the "binary" in a GUI app written with Python, it means Python GUI apps won't be able to enable Liquid Glass effects unless Python itself is compiled against a macOS 26 SDK. There's an Info.plist key (UIDesignRequiresCompatibility) to disable Liquid Glass effects; but no key to enable them.

AIUI, this doesn't impact on the minimum supported macOS version.

This was originally reported as a problem with BeeWare's Rubicon ObjC bindings (See beeware/rubicon-objc#648). Using a slider, a native app compiled against macOS 26 SDK looks like:

Screen.Recording.2025-09-21.at.13.36.56.mov

But, when using a pre-26 SDK, it looks like:

Screen.Recording.2025-09-21.at.13.40.22.mov

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

[freakboy3742]

@ned-deily I presume resolving this will require an update to macOS release processes.

[picnixz]

But, when using a pre-26 SDK, it looks like:

Out of curiosity, is it bad? is the issue the circle not being centered around the pointer? or the speed of the cursor being too fast?

[AA-Turner]

Out of curiosity, is it bad? is the issue the circle not being centered around the pointer? or the speed of the cursor being too fast?

The first video has the 'liquid glass' effects, see e.g. that the knob turns translucent when dragged, with the edges tinted blue on the left side. It's 'bad' in the sense that Python on {i,mac}OS will seem inferior/out-of-step with all other applications, which is a worse user experience.

Someone more au fait with Apple can make reference to the Human Interface Guidelines et al, I'm sure!

A