Not sure if this is a bug or not, and not really expecting any involved detective work, so maybe this is more of a feedback comment.
Recently installed Brave on my Windows 8.1 x64. I have a nvidia graphics card.
When playing DX9 and DX11 games, I can alt-tab back and forth between game and browser using Chrome with no issues. But if I try doing this with Brave, the game graphics will either crash, or change from fullscreen to windowed mode with significant lag before the game is playable again.
I tried disabling Hardware Acceleration in Brave, but still encounter the problem.