You system drive is virtually full. Yes, 80GB seems a lot, but is less than 10% of your 1TB, and you are dealing with video, so that may slow down things. Certainly make sure not to let the free space dwindle to much less.
Also: even if not being explicitly used, it is possible that the rotating hard drives may be causing slowdowns.
If you can edit for a bit without having them connected, you can test to see if that helps or not.
You have a few system extensions that are really old - 10.5 Leopard old!
And, as I feared... you have Chrome and its keystone daemons installed.
They break FCP by hogging the system videotoolbox.
In all likelihood this is the near cause of your troubles (I can almost hear you say "but I have had Chrome for years...", but believe me, this thing wreaks havoc on video applications).
See https://chromeisbad.com for why this is, and how to uninstall.
It is NOT enough to trash Chrome.
After uninstalling Chrome and its evil keystone things, you need to trash and redownload FCP.
This could be tricky! You are running 10.5.4 and you will get 10.6.1. I hope this does not wreck things like plugins that you have.
Make a zip of your existing 10.5.4 just in case.
Make sure to backup your libraries before opening them in the new version.
Finally, this is a clear symptom of the Chrome problem:
Diagnostics Information (past 7-30 days):
2022-02-16 11:18:42 VTEncoderXPCService - High CPU Use (2 times)
Executable: /System/Library/Frameworks/VideoToolbox.framework/Versions/A/XPCServices/VTEncoderXPCService.xpc/Contents/MacOS/VTEncoderXPCService
No Chrome in sight, but yes, it causes the VTEncoder service sweat!
