Final Cut Pro uses very little memory and CPU on my Mac

Background rendering that always complains it's not finished can mean that something in the cache has become corrupt. Select the library in the browser, choose File->Delete Generated Library Files... Choose All Render files.

Manage render files in Final Cut Pro for Mac - Apple Support  This does not delete analysis files though which may be what's getting hung up in this library. I always set the location of the cache to be outside the library so it's quick to delete everything. To set it to external, select the library and modify Storage Locations. Be sure to quit FCP before deleting the "[library name] Cache.fcpcache" file. Anything that FCP needs will be re-rendered.

Another easy thing to try when FCP behaves oddly is to delete the preferences. 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.

On a modern machine like this, background render should not be necessary in most instances. If there's an effects heavy section that can't be played in real-time, select it and press Control-R. Be aware, Smooth SloMo is very processor intensive and creates very large files.

Also, rendering prior to sharing is not necessary.

You have Chrome installed which is a known cause of issues with FCP. The background updating software seems to break the video toolbox somehow. Follow the instructions at https://chromeisbad.com for instructions on completely removing all the files that Google scatters across the drive. Simply removing Chrome.app is not enough. Best to reinstall FCP fresh from the AppStore since it's been known to be damaged by Chrome.

You also have a Cleaner installed, ccleaner. Another cleaner, CleanMyMac, is considered malware on this forum. Many here discourage any kind of Cleaner software since they are not necessary on MacOS and in the case of CleanMyMac can actually damage the OS requiring a reformat and reinstall. Perhaps the same is true of ccleaner, I don't know.

Finally, it appears that there are a few instances of old software installed. Did you migrate from an older Mac?

In addition to what the other contributors have said, I noticed one small thing in the report, that your WD Elements disc is operating at USB 2 speeds, which is very slow indeed. Do you have it attached to a USB 2 hub? I have a couple of them and only use them for archiving. They are slow discs anyway (they go to sleep and take several seconds to wake up!) so hopefully they don't form any part of your FCP workflow. The USB interface on mine works at 5 Gbps although you will never get that from the disc itself of course.

I can't say that this has anything to do with your experience but, as a test, you could disconnect all your external peripherals, set up a new user account with only FCP and see how a new test library performs with the internal discs.

Please provide more details about the project specs and complete footage specs to help diagnose. Also very helpful is an https://etrecheck.com report. Give the app Full Disk Access in System Settings and paste the report into your reply using the "Additional text" icon below. You can search other discussions to see what the anonymized etrecheck reports look like.

Photoshop should fly on that Mac, even if you were using huge multilayered 16-bit files with all that memory. That suggests something amiss with your OS install.

I would suggest following Terry's advice. Cleaners are totally unnecessary on Macs and can remove files that should not be removed and cause havoc. After removing these apps, you might also try Disk Utiility to run a First Aid check on your drive just to make sure the file system is ok. If none of that works, backup your data, wipe the internal drive and do a full reinstall without the extra stuff. That Mac should fly after that.

It sounds like you're experiencing a few challenges with your 4K video project. Here are some suggestions to address these issues:

1. Speed Changes and Video Quality: Since the "Best (Machine Learning)" option sometimes results in blurriness, try using "High Quality" or "Better Performance" settings instead. These might provide a more consistent result without the blurriness.
2. Background Rendering: Background rendering can be slow and may not always complete. Turn off background rendering and manually render sections as you work. To avoid the error about incomplete background tasks, ensure that all manual renders are completed before exporting your project. You can monitor this in the Background Tasks window (press Command+9).
3. Flicker in Final Render: Flicker in the final render but not in the FCPX preview could be due to a few factors, such as frame rate mismatches or rendering settings. Double-check that your project settings match your source footage's frame rate (29.97fps) and resolution (4K). Also, try exporting the project with different codec settings (such as ProRes) to see if it eliminates the flicker.
4. General Performance: If your Mac feels slow, ensure it has sufficient RAM (at least 16GB, preferably 32GB for 4K editing) and ample storage space. Close any unnecessary applications while working in FCPX to free up system resources. Using proxy media can also help improve editing performance, as it reduces the load on your system by working with lower-resolution copies of your footage.

Implementing these suggestions should help improve both the performance and quality of your video project. Thanks!

4o

Not all computational processes can use infinite amounts of memory and resources. If you're using the new AI features (as is obvious in your first image) be aware they take a good amount of time to complete, and create massive analysis files. When you say "less memory and CPU resources than expected", where do these expectations come from? This is just how computer programming works.

You should unmount the drive. It will slow the whole USB bus.