FCP 11 Suddenly Unusably Slow

Delete the application preferences. To delete preferences, hold down command and option while starting the application and click Delete Custom Settings. The application will start with default settings and open an "Untitled" library. Adjust the settings, reopen the library you were working, and see how it works now.

Delete All Render Files.

How much space on the system drive, and on the drive containing your media and library?

Low free space can cause tremendous slowdowns.

If you have adequate space, and the above did not help, then please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

You also have Chrome and its background daemons. They are known to hog the system videotoolbox and cause damage to video applications. You should completely uninstall - see https://chromeisbad.com

If you need a Chromium based browser, try Brave, Opera or Edge.

The first thing that stands out is that you should uninstall crowdstrike. Any third party antivirus or cleaners are not just unnecessary but hurt performance, especially for pro applications.