It's been a while since I've used Mirror Selected but I've never had a problem viewing the mirror at less than the source's framerate (that was on older i7 and 1080gtx).

Beta 4 here, getting maybe 3 fps using Mirror Selected on a YouTube videos, Twitch video, any DX11 or DX12 video game, locally saved video, even just scrolling my browser down.

I havent adjusted any Mirroring settings to my knowledge since this last worked properly so I'm not sure why this is ass. Any direction would be appreciated.

9900X3D CPU, 4060 TI GPU, 32 GB DDR5, SSD.