Hi Jim,
What about icons, etc., outwith PixInsight - such as on your main desktop? Have they remained the same size as well?
If they have then you need to sort out scaling at the Operating System level first. Once you have done that, you can tackle scaling within PixInsight itself.
When I upgraded my multiple monitor setup to 4K UHD monitors, I actually found that the test within PixInsight was too small for my tired old eyes, so I had to upscale that.
Hope this helps.