Lagging/Stuttering When Trimming & Extending Clips On The Timeline In Final Cut Pro

I would not use a third-party web-based trimming app. Trimming Long GOP formats such as H.264 or HEVC is tricky, and those utilities have a history of damaging files. Sometimes that damage is subtle and can manifest as odd performance problems.

You can safely trim video files locally using Quicktime Player. It can not only trim but can delete or reorder sections within the file and it does no-encode output so it's very fast.

See Apple MacOS User's Guide: Trim a movie or clip in QuickTime Player on Mac - Apple Support

For a video tutorial, Google or search in Youtube for "Easily Trimming Video Files With QuickTime Player"

In addition to joema's excellent advice to share samples for inspection, I see a couple things in the report even though they might not be related to the current issue you're experiencing.

One of your 2TB external drives has less than 10% free space. That's considered full.

You have Google's keystone and updater software installed. Follow the instructions at https://chromeisbad.com to completely remove all the software Google scatters across your drive. The keystone software in particular is a known problem for FCP.

Post an https://etrecheck.com report here using the "Additional text" button below in your reply. Give Etrecheck full disk access. This anonymized report can point out software problems that could be causing issues with FCP. Things like "cleaner" software, Google's keystone software, anti-malware software running constantly, etc.

If you could put on a file-sharing site and upload (1) A sample *original* camera file (2) The edited sample file which demonstrates the problem, and (3) The XML to load the edited file, we could examine it.

Your video metadata shows the original file has been re-encoded with an older version of an FFmpeg library called Lavf59.27.100. There have been previous problems with some of those.

I've been having an issue for a while where FCP stutters/lags when I'm extending or shortening a clip in the timeline.

In addition to the advice from joema and terryb, using shortcuts instead of dragging to expand and trim clips will make operations faster.

- Show the clip handles →Place the playhead where you want to cut →shift+X

- option+[ or ]

Thanks terry. Until those perfunctory things are handled, there's no need for painstaking, time-consuming technical examination of low-level items.