Yeah I've been in touch with Apple Support. Screen recording, etc. I pointed them to this thread to let them know I'm not the only one seeing this issue.
It's hard for me to believe that Apple wouldn't fix this is due time... or maybe I'm being overly optimistic.
I was running FCPX on my 2015 Macbook Air (Mojave) with limitations, of course... but it wouldn't crash with 10-20 minutes of use, which makes me believe this is definitely a software issue, rather than a hardware one.
I'll keep you guys posted on the efforts on my end; might try using Davinci or something in the meantime to confirm.
Are we even allowed to return FCPX after buying it in the apps store?