Getting the on screen keyboard to pop up from the bottom when focus is in text field in Windows 10 (like mobile)

Solution 1:

Built-in programs, and programs that correctly support touch on Windows 10, should pop up the keyboard automatically. Programs that do not support touch won't do so.

You might need to go to Settings => Devices => Typing and enable the "Automatically show the touch keyboard in windowed apps when there's no keyboard attached to your device" option (source). This might also be called "Show the touch keyboard or handwriting panel when not in tablet mode and there's no keyboard attached" on recent builds.

Additionally, you should have a keyboard button on the taskbar, between the notification area and the clock. This provides an easy way to bring up the keyboard for programs that don't auto-show it.

If the button is not visible, right-click on the taskbar (long-tap for touch) and select the "Show touch keyboard button" option.