This post was very helpful. My OperaGX suddenly jumped to eating all CPU unless I limited it, and even then it would eat every ounce of CPU within that limit. It was constant and restarting didn't fix it. This thread's advice to use the built in task manager (shift+ESC), that I didn't know existed, was exactly what I needed. I don't have screenshots, but I saw that the process using the most CPU and RAM was an extension process that had "background" in the title. I opened my speed dial and looked at my nifty animated background choking to death on itself and realized that was the problem.
It seems that Opera is still displaying the animated background across all tabs (of which I have many opened) regardless of if the background is actually visible or not. As soon as I disabled the animated background (all backgrounds actually) the CPU and RAM dropped instantly down to 2-3% from the 30% I had it limited to. I got another small drop by disabling the matrix widget. And then realizing I never use the widget on the speed-dial screen I just disabled widgets entirely. My system is performing significantly better now that I've turned these functionally useless frills off.
I hope this helps others who are running into the same issue to resolve it. It may just be that you have some useless feature turned on that is running wild in the background when it shouldn't be.
