No, I did not set it to 4 until I started trying to solve this issue. It had been set to automatic and when I upgraded the UI elements were too large, as I reported earlier.
To fix the problem, I set it to manual to try to fix. I first tried entering a value less then 1.0, which it would not accept. Next, I tried 2 and it seemed to make no difference, so then I tried 4.
The issue is that PixInsight is apparently NOT automatically setting it to 1.0 with my Display preferences configured as stated earlier. It is apparently automatically setting it to 2.0. So, I finally figured out that if I set it to 1.0 manually and keep the automatic scaling turned off, the UI is properly sized.
I was just going to answer your question: the configuration file is Library/PixInsight/PixInsight.plist on your home folder.
I don't know why you had a UI scaling factor of 4. Did you set this factor manually before running this version?