Thank you again, Jo! Saw your post on fcp.co.
Here’s what I replied there, for other Cow users:
Thank you Joe for the rundown of so much sound advice. I have been using 90% of those procedures you mention, so it’s also good to know I am on the right path. It’s very strange, for me, how it takes SO long to rebuild these waveforms. I have left FCPX alone for several hours, several sessions, and it still is rebuilding them. Every now and then a clip previously with red waveforms becomes complete. One by one, very slow, and I am on a not-so-slow 2019 Mac mini.
About Catalina and FCP 10.4.10, I di not know there was that update, will look into installing both on my 2017 MBP and see how they go. I would love to upgrade fully, but mid project and with 32-bit apps that I still like to use, I will not upgrade yet on my main machine (Mac mini).
Thank you!