The application you have opened with an Open step is not active.
Please refer to the following solution.
・To activate an application, you should either click the title bar or add a step that selects its icon.
・Set the target application in the "Application" area of the step.
■If you launch the calculator and the Notepad, then execute a "Press Key" step on the activated calculator.
Even if you set "Notepad" in the "Application" area of the "Press Key" step, your manipulations will be performed on the calculator.
■If you add a "Click" step before the "Press key" step
Adding a step that clicks the Notepad title bar before the "Press Key" step will make the Notepad active, and values will be entered in the Notepad.
An Open step does not always mean an open application will become active.