You can’t.
That message has nothing to do with Uphold. It’s Brave’s decision. Check their list at https://support.brave.com/hc/en-us/articles/6539887971469
That is Rewards, which means you see ads. That has nothing to do with linking to Uphold or Gemini. They are two different things. The difference is one lets you see ads and earn BAT. The other one is about being able to link to a custodial partner and move the BAT outside of Brave.
You also may be interesting in my topic which I post regular updates on the status of countries. I try to get info at least once a week and will also post/update on it if Brave adds or removes any regions. That topic is at PSA: Unsupported Region