I don't know what changes you've done to your browser regarding streaming videos but I've noticed over the past few weeks or so that when using YouTube it's become very laggy, Videos are slow to play when scanning forward or backwards and even typing a message in the comments section it's delayed when hitting a key and the text showing up on the screen.
It never used to do this so I'm assuming something must have changed in the recent updates in your browser. I looked in task manager in Windows 11 and Opera internet browser is using almost 2GB in memory. It has a number in brackets after it saying (27) whatever that means. I've cleared the cashe and gone back to default settings and it still goes back to doing this.
I tried Microsoft Edge and YouTube works better there with only around 7-800MB in memory. Any ideas why it;s doing this?