Prominent , just create a file named installscript.vdf and call your .bat file as uninstall process
Doc: Steamworks -> Making and using Install Scripts -> Run Process on Uninstall.
MadSpy oh man, thank a lot, I understand how to make it!
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MadSpy, where/how to create steam uninstall script? I don't see anything in the steamworks pages to do that, and no information anywhere on how to do it.
Read the page where the instructions on making install scripts are more carefully.