FCPX 10.5.4 download

There is no 10.6.4 yet, so I assume you mean 10.6.3.

FWIW, I have an identical mac to yours, except that I only have 16GB of RAM, and FCP still works as always.

Most likely there are other issues - note the word "lately", which suggests that something has changed.

You should tackle this. In order for us to have a better idea of what may have caused this, we need more information.

Please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

Also: which drive has your media and libraries, how is it formatted, and how full?

Do you have any "antivirus"? Do you have Chrome?

We don't know what Apple knows, but it's always a good idea to use feedback to report issue with as much detail as you can fit in the small space allowed.

You would need to download Catalina and put it on a bootable jump drive to install that OS on an external drive. When booted into that drive you'll be able to download 10.15.4 from the App Store. (It's always a good idea to keep copies of older versions of key applications.)

You'll have to use XML to export from updated libraries to get back to the older version.

You have CleanMyMac which many around here consider malware. It's possible that simply uninstalling it and reinstalling FCP will help but there have been many cases where CMM has damaged the system and a clean OS reinstall is necessary. You can search here for CleanMyMac to read more about it.

Also, Chrome and its keystone daemon and agent are installed. Chrome breaks the video toolbox and is a known cause of ProApps problems. To completely remove, follow the instructions at https://chromeisbad.com. Simply removing Chrome is not enough. After removing Chrome and its keystone henchmen you'll need to reinstall FCP.

And finally,

Security updates disabled - Security updates are disabled. This computer is at risk of malware infection.

Apple security disabled - Apple security software is disabled. This computer is at risk of malware infection.

If you keep Chrome and especially the keystone daemons you are shooting yourself in the proverbial foot.

See https://chromeisbad.com for an explanation of what they do. At the very least you should remove all the keystone things. They exist ostensibly to help keep Chrome up to date but they cause the problems described in the site linked above, and Chrome can be used without them; but really do you want to?

This tells it like it is: https://contrachrome.com

If you need a Chrome based browser that does not do all those evil things, there are plenty of options, too - Edge, Brave, Opera…

or use faster, cleaner browsers like Safari or Firefox

When you restore make sure it's *only* your User data, no Applications or anything else. If you do, then you're just transferring the problems back onto your clean and fresh OS. Download your apps from the App Store again and directly from 3rd party developers.