FCP running extremely slow

Hello everyone. I’m hoping someone can lend a hand here as I am truly lost for what to do. Final Cut Pro is notorious for not running super optimally if you don’t take certain steps but this is another level.

I launches and loads the project pretty much immediately however whenever you try to edit it in any way (trying to watch it, make cuts, add transitions, etc…) it takes like 5 seconds of buffer time before it does the action.

Originally I thought this was a hardware issue as my wife does (and has done) all her editing on a 2017 MacBook Air. She has never had this issue in the past despite doing similar videos so we just assumed the laptop was dying. So we booted everything to an iMac that is much more capable and nothing changed. Despite having extremely low CPU and Memory usage it doesn’t run any faster.

She is very diligent about using and clearing out her libraries, giving her drives a comfortable amount of space (50+ Gigs), and what not. Background rendering is off.

The only thing I can think of is

  1. She is currently running on iOS 12.7 since the MacBook Air is so old. I’m not sure why this would just suddenly cause issues though as she has never had this issue previously despite, as I have stated above, having done very similar videos previously.

  2. She needs to start using proxies. This seems viable but again I don’t know why this would just suddenly cause issues half way through a project.

Any advice would be appreciated, we’re looking into getting her a M1 laptop soon because she desperately needs an upgrade anyway but I don’t think it will fix this issue so I’d like to resolve that first.

Thanks in advance.