Custom NSWindow styleMask behavior changed/broken resulting in unresizable or non-responsive windows in macOS Tahoe 26.3 RC

Question

Created 5d

Replies 6

Boosts 6

Participants 5

NSWindow objects with custom styleMask configurations seem to behave erratically in macOS Tahoe 26.3 RC.

For example an NSWindow is not resizable after issuing .styleMask.remove(.titled) or some NSWindow-s become totally unresponsive (the NSWindow becomes transparent to mouse events) with custom styleMask-s.

This is a radical change compared to how all previous macOS versions or the 26.3 beta3 worked and seriously affects apps that might use custom NSWindows - this includes some system utilities, OSD/HUD apps etc, actually breaking some apps.

Such fundamental compatibility altering changes should not be introduced in an RC stage (if this is intentional and not a bug) imho.

Boost

Answer 1

Steve4442 OP

5d

FB21879057

1

Answer 2

Frameworks Engineer OP

Apple

5d

Hi Steve,

Thanks for the Feedback number. We've gotten a few similar reports on 26.3 RC and are investigating.

4

Answer 3

pawelmtw OP

5d

@Frameworks Engineer

We also encountered an issue with transparent NSWindows on 26.3 RC (FB21879511).

On 26.3 RC, mouse events are intercepted by the entire transparent window rather than only the opaque regions. As a result, any third-party app that uses full-screen overlay windows blocks system interactions while the overlay is present on the screen.

0

Answer 4

Steve4442 OP

5d

I am super relieved it's not only me hallucinating all this and others encountered this as well. :)

I narrowed down the issue to .styleMask.remove(.titled). Depending on other styleMask flags and NSWindow properties, this can result in (1) an inability to resize the window or (2) a kind of click-thru effect - the content does not seem to capture mouse events but the window acts as if it would be transparent to user interaction.

2

Answer 5

ChenPM OP

4d

We are also affected by this issue.

All borderless windows are no longer clickable or movable in macOS 26.3 RC. This behavior was working normally in 26.3 Beta.

3

Answer 6

zwaugh OP

3d

We're experiencing this in our app as well, macOS 26.3 RC has completely broken the interaction of being able to click through transparent areas of a borderless window that worked in all prior macOS versions.

2