SUMMARY
Spectacle is failing to record WebM/VP9 video for me. The issue I'm reporting is its "Temporary file URL must be an existing local file" error message is unrelated to my apparent actual library problem.

STEPS TO REPRODUCE
1.  Run Spectacle from the command line.
2. Choose any of the New Recording options and start recording.
3. As Spectacle says, click the pulsing red circlular system tray icon to stop recording.

OBSERVED RESULT

An error dialog appears containing:
    Failed to export video: Temporary file URL must be an existing local file

Spectacle's terminal output ends with the following, the first line is red:

[libvpx-vp9 @ 0x7f7464119740] Failed to initialize encoder: ABI version mismatch
kpipewire_record_logging: Could not open codec Invalid argument
kpipewire_record_logging: No encoder could be created
Failed to export video: Temporary file URL must be an existing local file

EXPECTED RESULT
I assume I have a library problem with "WebM/VP9" format, as ffmpeg command line also fails with a similar "Failed to initialize encoder: ABI version error. I'll troubleshoot this (it may be a Fedora packaging bug and bug 485733 seems relevant).
But regardless Spectacle should report the actual underlying error or "video encoder issue", instead of misleading users about temporary/local/network files. The latter is not the problem here, nor was it the problem with bug 485733.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 41
KDE Plasma Version: 6.4.4
KDE Frameworks Version: 6.17.0
Qt Version: 6.8.3
Kernel Version: 6.15.9-101.fc41.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 4 × Intel® Core™ i5-6300U CPU @ 2.40GHz
Memory: 8 GiB of RAM (7.6 GiB usable)
Graphics Processor: Intel® HD Graphics 520
Manufacturer: LENOVO
Product Name: 20FN002JUS
System Version: ThinkPad T460

ADDITIONAL INFORMATION
I apparently made a successful Spectacle screen recording in .webm format in December 2024, saved to $HOME/Screencasts/Screencast_20241224_191731.webm , which is still the configured location for Spectacle videos.

If I change the video file format in Configure Spectacle > Video Saving from WebM/VP9 to Animated WebP (better than GIF) or MP4/H.264, then screen recording works fine.