Here are some steps to check the generation of the .cs file:

• First, make sure you have installed the Input System package, and it is up to date. I would recommend version 1.4.4 or later.

• In the Inspector, click on the .inputactions file and in the inspector, make sure Generate C# Class is checked, and check for typos. Click Apply on the bottom right. This should normally generate the C# file for you.

• If it didn't happen, you can right-click the .inputactions file and click "Reimport" to double check.

• If that doesn't work, it might be that it is turned off in the global settings. Check this feature under Edit->Preferences->Input System