Once you've connected a custodial account—such as an Uphold, Gemini, bitFlyer, etc. account—to your Brave Rewards profile, you won't be able to go back to the original non-connected Brave Rewards state on your current Brave Rewards profile. However, you can always reset Brave Rewards and start with a new Brave Rewards profile that isn't connected to any custodial account. Learn more about resetting Brave Rewards, here.
I disconnected Brave Browser on my custodial account provider's website. Why is my account still connected to my Brave Rewards profile?
If you log in to your account on your custodial account provider's website (like Uphold.com, Gemini.com, etc.), you may find a section in your account settings that lists an application called "Brave Browser". Deleting "Brave Browser" from this list or revoking access does not disconnect or remove the connection between your Brave Rewards profile and your custodial account.
What does deleting or revoking access to the Brave Browser app do?
When you delete or revoke access to the Brave Browser app, the current authorization session your Brave browser has gets expired. You will then see "Logged out" messaging appear in your Brave Rewards interface.
Being "Logged out" means that the Brave Rewards feature in your browser will be unable to fetch your current BAT balance from your connected account. It also means you will be unable to send BAT contributions with the BAT from your connected account. However, on Brave's servers, your Brave Rewards profile is still considered connected to your custodial account.