@RasheedHolland I'm surprised as well, but it was right after I updated the driver that Vivaldi didn't slow down after a certain time anymore. I also have a Nvidia GPU + Intel integrated graphics. If I remember correctly, I had already tried in the past to force Vivaldi to use the GPU but it didn't solve the problem (though I'm not sure if I did correctly).
Just upgrade your Intel integrated graphics' driver, it's worth a try!