The BAT in your Brave Rewards wallet is vBAT (virtual BAT) and has no monetary value. It is like a game currency or a rewards program and just like in those systems you are limited on how you can use them. It is only when you send it to a custodial account that it is converted to the actual BAT token. The BAT token can be bought, sold, or swapped and has a monetary value.
Disclaimer here, I am not in any way shape or form giving you tax advice! lol Saying that, I would look into the taxing authority regulations for gaming/reward programs and find out what the reporting requirements are for virtual currency.
This is a recent topic post explaining in more detail about vBAT and BAT in general. Just be cautious when reading, sometimes the distinction between vBAT and BAT is blurred.