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I'd like to have Cfw on my 3ds xl (new model) or at least use my gateway card but my firmware is not supported for either Cfw or gateway I was told I can downgrade but I'm not sure if that's possible or how can anyone help me put it would be much appreciated

Here are many tutorials about how to downgrade your 3DS on gbatemp and i just find one. You can search the titile：
Simple Guide to Downgrading your 3DS