It depends on origin. Many of the times, it’s announced here on topics. But in other cases, it’s done through Brave’s site, just like the link I shared in my previous comment.
In some other situations, places like Gemini sent out emails. For example, I shared a copy of emails being received by people in a topic here at PSA: Venezuela no longer supported by Uphold (or Gemini)
And then I also shared notice that had been given to people about Russia at PSA: Uphold stopping Russia service
I shared information from a Reddit post made by the Rewards product manager at PSA: More info on Unsupported Region
You had Community posts by Brave to advise of issues with Uphold and Gemini at NOTICE: New region restrictions on verifying Brave Rewards with Gemini and NOTICE: New region restrictions on verifying Brave Rewards with Uphold
Then I maintained a topic that I kept editing and adding. You can track through all announcements being given. PSA: Unsupported Region
But some of the more important would be the two by support, the new region restrictions on Uphold and Gemini. If you read through it, you’d see where they said no new connections could be made and anyone with existing connections would be unable to reconnect if they became disconnected. So this let existing people know that they would/could eventually lose access to withdraw BAT and that their regions weren’t supported.