A few notes for you:
1. Spinning Pizza: I've never heard it called that before!
This is normally called the "Beach Ball"; of course I knew what you meant. Beach balling normally means that the system itself is busy in some way, which normally indicates a problem of some kind: Stuck program, stuck operating system, I/O problems (spinning up a drive), etc. It's definitely not normal to get a beach ball with MC very often at all.
2. When you create a new library, it's kind of confusing. What MC means when it says "create new library" is: "Find me a place to put the DATABASE FILES for this new library". The database files should be all by themselves with no media an no other files at all! But it's a very common thing for people to try to tell MC to put those with their media because that's how people think. If you have mixed database and media files together, that's a big no no and might be causing your whole problem. Try to create a library on your internal drive in a brand new EMPTY folder. Once that succeeds you can then use Tools > Import to add some media to that library. Note that "add some media to the library" does NOT mean copying the files. It just means telling MC to read the media files and learn their metadata (artist, album, song, etc). MC will add that stuff to the database, but the database files will stay all by themselves in that directory you created.
3. It's a little odd that you had this same problem with MC23 but that "an update fixed it". I assume you mean an Apple OSX update? That makes me suspicious. I would be inclined to back up all my stuff and rebuild the Mac from scratch from the recovery system. You will, of course, have to make your own decision on this drastic action that I'm leaning towards. I'd be comfortable with it, but a lot of people would not be.
Good luck.
Brian.
