Windows 10 on 900p monitor

Just guessing this is what you need.

1) right-click desktop... change the DPI scaling if you want but for 1600x900 I'd stay with default

2) open CLEARTYPE if you have software with text issues

3) SCROLL + ALT to change browser page scaling

Other:
If you haven't done so the monitor or GPU should be set to scale by aspect for games with a different resolution. For example, on the monitor itself if you set scale by aspect, then if you had a 1024x768 program it should fit the HEIGHT of your monitor (1600x900) and have black bars on left and right, but would NOT be stretched.