How to send a keystroke to a background application or process?

Question

Python

I used robot.js on the node, it presses the keys perfectly, but the problem is that it does this without being tied to any process, that is, it emulates just pressing.
I read about sendkeys in python, where it can cling to a window, but when you need to press a button, it expands this window, which is naturally not good.
The question is whether there are such libraries or examples of ready-made solutions for this task in these two languages ​​specifically (node ​​or python, well, you can also use the Windows command line, but I’m completely xs there). Google does not want to issue anything sensible, on requests for sending keys to a background application. How to be?
The task is simply to send pressing F9 to the d3d application. Various clickers like ahk, autoit, uopilot etc don't work.