Am I the only idiot that has upgraded to Catalina?
My set up is:
MacBook Pro 2018, 6 core running Catalina 10.15.1
Blackmagic eGPU Pro with BenQ 4k Monitor
FCPX crashes every other time on start up, and every time I quit. I have updated the apps that are 32bit where possible but some are still not 64bit. iZotope is not yet compatible with Catalina so that might cause a problem but who knows... anyone?
I don't have that exact setup but one of our computers Macbook Pro running Catalina is working fine. If you haven't done this already, try relaunching FCPX while holding OPTION and COMMAND keys to clear preferences. This is generally recommended when first launching an updated FCPX especially on an updated OS.