I've had slow downs before after upgrading OS X but this Catalina update takes the cake as the biggest performance hit yet after an upgrade when it comes to FCPX. Every edit includes a spinning wheel wait now. Every edit on HD or 4K, proxy or optimized. What is going on? This (was) a fast enough iMac that meets the requirements as far as I know.
iMac (Retina 5K, 27-inch, 2017)
4.2 GHz Quad-Core Intel Core i7
32 GB 2400 MHz DDR4
Radeon Pro 580 8 GB