SketchUp 2017 will appear blurry and pixelated, but all items at correct scale. An app that only knows how to draw itself on an low-resolution display will think it is on a low-res display, then the operating system takes the app’s image and upsamples it. What you can do is to change DPI settings for legacy apps. It won’t ever change for older apps, even if your operating system is updated or your display replaced.
The improvements in your SketchUp 2019 do not automatically appear backported in SketchUp 2017.
Are you aware that support for high-resolution displays (or better to say for the UI scaling factor) has been gradually introduced starting from SketchUp 2016 to SketchUp 2018? That means SketchUp 2017 has limited support and some items are in wrong scale.
