Three Ways to Display Universal Windows Apps (Windows Store Apps) Full Screen
Universal Windows Apps or modern apps in Windows 10 can be resized or used in full screen.
There are three ways to switch between windowed and maximized.
Video tutorial:
1: Press the Shift + Windows Key + Enter to use full screen or again to return to minimized.
2: Press the arrow icon in the top-right corner to use full screen or again to return to minimized.
3: Press Menu in the top-right corner. Scroll down, and click Full Screen View or Windowed View.
If your current UWP is already in a window, you can customize the exact size.
Line your mouse at the top, side, or one of the corners until the cursor becomes an arrow. Hold down the left mouse button and move to the size you want.