It is because Brazil is unsupported for verification of Brave rewards. Don’t confuse this with you not being able to do any transactions on Uphold. Brazil not being supported for rewards verification was mainly a Brave’s decision which was backed by Uphold & Gemini. They’ve stopped supporting a lot of regions because of regional rules & regulations, frauds and a lot of other reasons.
Brave is working on enabling support for most workable countries by the end of this year with Brazil & India being top priorities. Right now, they are working on Brazil and then they’ll turn to India.
You will get more info at PSA - Unsupported regions