How to make Automator auto press a key on a different application?

Try a macro creator like Keyboard Maestro. It can do what you want and much, much more. I have over 100 macros created with it from launching apps, changing settings in Safari to posting text with a simple text imput. When I forget the keystroke it's easy to do a search in Keyboard Maestro to find the right one.

There are other macro apps in the App Store but KM is the most powerful.

Automator cannot send real keyboard input to apps that require raw, low-level key events — especially games.

Mouse clicks work because they use a different (and less restricted) event system.

I have not tried with games, but Automator, with the help of Applescript, CAN send keypress events (assuming all the necessary permissions are granted).

Here is a small example. I think you can easily guess exactly what it is doing, as the syntax is so clear.

When I entered your topic line into a Google search, its AI it presented me with a proposed way to do this. I didn't test it but have found that even if some of the scripts it proposes do not work outright, they can after a bit of tweaking. The solution used both Automator and Applescript.

I am wondering why you don't just press the key yourself? To activate the automator step you have to use a shortcut.