In your browser. Any vBAT you had wouldn’t have disappeared. And anything you earned prior that was sent to Uphold or Gemini would still be there.
The only way it would be gone is if you reset Rewards, uninstalled Brave, factory reset your device, or if you sent it as tips or left auto-contribute on.
Maybe? I mean, if they happen to add your region again before they finish sunsetting vBAT then you’ll be able to withdraw it there. Otherwise you can count everything you had earned as “lost” if you haven’t given it away to anyone.