Doesn't look like an answer has been provided on this! I've been going through the same issues, and I think I found the solution (or a solution for some at least):
This was what really solved it for me 100%: I had iCloud sharing enabled for my desktop, which makes your whole desktop synced with the Cloud all the time (if you have Cloud services from Apple), so I disabled that:
click the Apple logo > System Settings > Yourself > iCloud > iCloud Drive > Turn off Desktop and Documents Folder. It might take some time for it to unload and such, but for me now not only is everything on my desktop fast again (I have all my developer files on my desktop), but now Xcode is super fast and everything works with zero crashing.
My thought is that when I tried to create a new project and it asynchronously was trying to open for the first time AND upload to the Cloud, well, it seems was just giving up before it even started.
Hope that helps!