Thanks for the information. This is very discouraging, to say the least. I was hoping my new 16" maxed out M1+, which is in the mail to me for early December delivery, would handle it easily. Sounds like it is time to go to Davinci Resolve or Premiere as the path now.
I have never been a fan of Premiere since it exhibits all the user-viscious interfaces Adobe loves to consistently build into all its products. Davinci Resolve, on the other hand, seems to be the love child of FCP and Premiere. Making the transition (major FCP plug-in investments already made and now down the drain not-with-standing) will not be all that daunting.
Suffice it to say, Steve would never have allowed a useless set of two consecutive releases like this to happen. The entire FCP dev team (and Product Manager, in particular) would have all been fired by now. I am at a total loss to understand what is happening on the FCP dev team. Was the new built-in motion-tracking their downfall? What was it? They should have left things at 5.4ish before they were absolutely certain that had an app that, at the least, works. FCP has had some near-death calls as a product in the past when Apple went to the new FCP interface. It was at that time almost all film schools threw it out and went back to Avid or Premiere but it had grown back in popularity, since then. So this is a huge setback. The transition to Davinci Resolve will not be all that hard. I recommend at least trying it out since it is free.
Now all I need to find out first is if Davinci Resolve has the same performance problems on the new M1+ platform. Based on data I have collected thus far it seems it is fine but merits further investigation. I know Premiere runs OK on M1 based on what I have heard. Davinci Resolve seems to beat it out in certain benchmarks (e.g., rendering time). But that is for other Forums to pursue :-) This transition seems like losing an old friend. Shame on the Apple FCP team and what a major defeat and setback for Apple and its FCP user base. But they have iPhones to sell so FCP must once again be the ugly step-child product these days.