See Hardware Acceleration - Frame drops on Twitch/Youtube - #4 by Saoiray
Currently on Windows you need to set application specific settings in the graphics driver (on nVidia at least) for brave.exe. Sounds like your issue revolves around “monitor technology” or vsync, background FPS limit, FPS limit, or all of those.
Brave should do a better job at controlling these settings for the user, other browsers tend to do a better job at the moment.
I immediately had FPS issues when using youtube hardware accelerated in Brave, my issue was the FPS limiter in the nvidia driver but yours might be different.