you know. I think there might be this reason as to why your opera GX isn't using your gpu(anytime at all), and why it is using your CPU. so, CPUs can be used to render everything too, except they're much slower cause they're not meant for it. so I think the reason it's not using the gpu is- a lot of the other applications are using the gpu at that time maybe? and so it switches to the integrated and the CPU. so you should see that all other apps(even the epic store), or anything that might use your GPU, off at that time.
You can also try resetting the apps that are set to dedicated gpu if you don't need them on that. And, aha! also put the default gpu to integrated as most apps can use the integrated(even apps like zoom and all). this tip is to be used at your own convenience, but I recommend it as it might just be the reason your opera GX isn't using it.
And remember, to turn hardware acceleration back on.
Sorry for the late reply, I was thinking about this issue only, but couldn't get much of an answer. Try what I told you above though, I think it might work(there can be a high chance)