If all you get is a template answer, you will never get what you are looking for.
It means they found enough evidences not to unflag your profile. Your only option is to move on.
Only advice I can give you is to be more careful next time and never try to cheat a system, or the system will cheat you.
Find below the official reply to my support ticket. It neither states any information that I did not already have before, nor does it give me any hints how I can appeal this decision. (Or at least, how can I set up a new reward id?)
What is the claimed " irregular activity"? I have just used the Brave browser as any other user.
Month for Month my rewards are vaporating.
Thank you for reaching out to Brave Support.
Sometimes your Brave Rewards profile can be “flagged”. That usually means our systems noticed some irregular activity associated with Brave Ads. “Irregular activity” is activity that would be considered unusual compared to an ordinary person using Brave Ads as part of their overall, everyday browsing experience.
Your wallet was flagged for irregular activity. It will not be reinstated.
Thank you again for understanding and patience as we work to improve the ecosystem for all users.
@Wallenstein They gave you one of the answers I said that you’d have gotten.
This means you violated Terms and in such a way they are confident it was intentional. Most likely it was fraud.
If you want to know how you got caught, you’re out of luck. Nobody tells you. Doesn’t matter if it’s Brave, Uphold, Gemini, Binance, or any other business. For example, here are similar complaints from people that had similar happen to them on Binance.