What I meant is, if the game still complains about no internet after you erased your wi-fi credentials, you should uninstall the game and everything related to it, including tickets. DBI, which I highly recommend, can do that. Check these
instructions and try to apply them to your Switch. After all this is done, normally, if you re-install the same game, it will have no recollection of ever having been installed before on your console. Therefore, it will not assume you have internet enabled, and seeing that you don't (wi-fi is off) it would launch without complaining. That's the theory. Hopefully, it will work. Personally, I use fusee.bin to launch Atmosphere, not fss0. Maybe that makes a difference?