Final Cut Pro performance issues on macOS Sequoia

We're going to need a lot more information to help you diagnose what's going on with your system. Post a report from https://etrecheck.com using the "Additional text" button below in your reply.

An easy first thing to try is to delete FCP Settings. Hold Option and Command while launching FCP and choose Delete Preferences. It will open the default Untitled library. Re-open the library you were working on, set the Preferences back to the way you like them (disable background rendering, reset Import to Leave Files in Place, etc.) and see if the issue has been resolved.

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