Created attachment 182576 [details]
screenshot of the issue

SUMMARY

After updating to Plasma 6.4, Spectacle has a new toolbar with a button that says "New Screenshot". Using this button to capture a rectangular selection or the full screen will capture a window that still contains the menu, because it takes a brief moment to disappear.

STEPS TO REPRODUCE
1. Open Spectacle.
2. Click the New Screenshot button which opens a dropdown menu.
3. Click rectangular region or full screen.

OBSERVED RESULT

The menu you just clicked on is captured by Spectacle.

EXPECTED RESULT

It isn't captured.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.4.0
KDE Frameworks Version: 6.15.0
Qt Version: 6.9.1
Kernel Version: 6.15.3-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 5625U with Radeon Graphics
Memory: 43 GB of RAM (40.8 GB usable)
Graphics Processor: AMD Radeon Graphics