If Uphold will not provide you more information or respond, there is really nothing Brave can do. Brave and Uphold are two separate business entities and Brave has no control over Uphold’s business decisions. If you live in a country with consumer protection laws, that may be a route you want to explore per your Uphold account.
Is Gemini available? You could verify with Gemini if it is. Otherwise, if ad campaigns are available in your region and you are eligible to receive them, you can still receive ads and earnings. You Rewards will be unverified and can only be used for auto-contributions/tipping for now.