Thanks for the advice and info. I went back to the App Store and as before it told me that I could not run V12 on my system. Two days later, I got an update notice that I have two apps that can be updated. One of them was Logic, and it was V12.2. I tried updating it and was told Logic Pro could not be downloaded. So, I turned it off and turned it on again, and now it downloaded, installed, and reconfigured my Sound Library. Starting V12.2 up, it validated my plugins, including some that never worked in V10. So, all looks good so far. It does run on Intel, even if some features don't.
At this point, I'm trying to figure out what it did with my sound lib. Settings tells me it is still on an external drive where I put it. (my internal drive is not that big) But there are a few things that look odd. Logic report that getting everything in the new sound lib needs less than 50G, but my current lib is well over 60G. I need to find something gives a good explanation of the sound lib, how to manage it, how to make sure it is where you think it is, how to see what's in there etc.