Just wanted to join the chorus of boos on how disappointed I am that you haven’t yet updated the interface for 4K users. The issue was raised in June 2018!! I had the free version for years and bought the collection in good will that you will be updating it, seems like you have just bought it for a quick buck and haven’t done anything with it as far as I can tell.
I have found the solution for the tiny size of the Nik Software in windows 10 with 4K monitors.
Find the location of each of the Nik software applications exe files
By default is should be C:\Program Files\Google\Nik Collection
right click on the exe file
select properties from the drop out menu
select compatibility tab (near the bottom of the compatibility tab you will notice “Change high DPI settings”
from here check the box for Program DPI, click OK
Click Ok on the file properties
Open the Nik software applications your scaling should be back to normal.
Still trying to figure out the photoshop plug-ins though…