FCPX crashing when deleting captions or editing them

Lots of crashes of different applications.

If it were me, things I'd try:

• Make sure you don't have iCloud Files enabled for your Desktop or other places you are storing media or FCP libraries.
• Create a new admin user, login as that user, create a new FCP library with a few clips and subtitles and see if there's any difference.
• Check to see if there's a corrupt font. Install and validate fonts in Font Book on Mac - Apple Support
• Run fsck on your boot drive. Reboot and hold the shift key down until you get to the login screen. Then reboot normally.

Please post an EtreCheck report https://etrecheck.com giving the application Full Disk Access in Privacy & Security System Settings. Copy the report and use the Add Text button to paste the result into reply box. 

Export the loaded SRT file. Does it crash when loading an exported file?

Sorry for the delay.

I can see that there have been many crashes:

2023-11-21 19:44:37 iOSScreenCaptureAssistant Crash (70 times)
    Executable: /System/Library/Frameworks/CoreMediaIO.framework/Versions/A/Resources/iOSScreenCapture.plugin
    Details:
      libdispatch.dylib: API MISUSE: Resurrection of an object

  2023-11-21 19:43:27 Final Cut Pro Crash (17 times)
    Executable: /Applications/Final Cut Pro.app
    Details:
      libsystem_c.dylib: abort() called

  2023-11-20 22:54:27 WallpaperVideoExtension Crash
    Executable: /System/Library/ExtensionKit/Extensions/WallpaperVideoExtension.appex/Contents/MacOS/WallpaperVideoExtension

They are probably related to one another.

Regarding third party software: I am not a fan of NordVPN or any other "public VPN" from a security standpoint, but I cannot see how it would play a part here.

Also: since the problem occurs with captions, and as such it has some relation to text, it may be worth opening Font Book and validating your fonts. A corrupt font may cause a lot of trouble.

I go to edit the SRT captions that I've imported, it shuts down the software.

What is the current library capacity? FCP often becomes unstable as the number of generated files increases.

Don't forget to delete the application preferences whenever there is a crash. Corrupted preferences subsequently can cause further crashes.

I will also have a look at the Etrecheck report.

As the name indicates, iOSScreenCaptureAssistant appears to be related to iOS devices.

I would expect to help when using your iPad or iPhone to annotate screenshots in your mac.

This is something that works extremely well - you take a screenshot in your mac and can immediately annotate with your Apple Pencil, for example.

HOWEVER, even though I tried this (and it works) on both my macs (Intel and M1 Max) running Sonoma, I do NOT have any "iOSScreenCaptureAssistant" process in either of them...