How do you make the Minecraft full screen window full screen on Windows 10?
You could try using the maximize button (square, just in case anyone doesn't know what it is,) but I assume you may have tried that. You could drag the window to resize it. If pressing F11 doesn't enter fullscreen, or makes it borderless, perhaps a reinstallation for Java or Minecraft could be done. Considering you've done these, look into Mojang/Minecraft official support. Considering that they made the game, they'd be the most efficient choice of support for your issue at the Minecraft Help Page