That is a HUGE amount of scaling, any reason why you have it so high? You are essentially running Windows at 720p with that high a scaling setting, which is quite a waste of a 4K screen. I am running my 4K screen at 150% scaling which works out at 1440p, and that works fine.
And set to 200% which is 1080p,
I do see the same as you at 300% 720p, but ill be honest and say it looks awful everything is so pixelated, especially text, quite a waste of a good screen if you ask me.