You can't start an app on the client machine without jumping through some real hoops, and having admin control over the machine - which is not the default for good reason.
Certainly, you can't start a WinForms app on a client until the client has logged in, as there is no way for it to interact with a user until then.
A much, much simpler approach is to have it installed to boot on startup:
How to launch application at logon/startup[
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