I have a Gemini account...why can't I just link it?

Because Gemini isn’t allowing new connections. If you were to Search Before Posting you’d see topics like PSA: Known issue with Gemini (Gemini is down)

And if you checked https://support.brave.com/hc/en-us/articles/6539887971469 which has a list of supported countries and all, you’d see:

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