SUMMARY
After the last update, Spectacle was capturing its own window in the Wayland session. The log included this message:
QVariantAnimation::setDuration: cannot set a negative duration

It seems that in the SpectacleCore::takeNewScreenshot function, the timeout variable was set to -1 and passed to the m_delayAnimation->setDuration(timeout); function, causing the issue. I went to the configuration file and removed the "captureOnClick" option. After that, everything worked fine.

[GuiConfig]
captureOnClick=true
quitAfterSaveCopyExport=true

Simple check like:
if (timeout < 0) {
    timeout = 0;
}

Also resolves the issue.

STEPS TO REPRODUCE
1. Update ArchLinux to the last version
2. Open Spectacle
3. Do, for example, fullscreen screenshot

OBSERVED RESULT
Spectacle is not hiding while taking a screenshot and appears in the screenshot.

EXPECTED RESULT
Spectacle should not appear in the screenshot.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.2.1
KDE Frameworks Version: 6.7.0
Qt Version: 6.8.0
Kernel Version: 6.11.4-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 9 7940HS w/ Radeon 780M Graphics
Memory: 58.6 GiB of RAM
Graphics Processor: AMD Radeon 780M
Manufacturer: Micro Computer (HK) Tech Limited
Product Name: Venus series