After some fiddling with my Opera settings I re-enabled GPU support for Youtube and other web related stuff.
I have old AMD APU A10-7850K on FM2+ socket, which is having integrated graphic but I don't longer use it. Instead I have also dedicated simple graphic card AMD Radeon RX 570. That all is running on Windows 10.
Sometime from Opera 89 and up (now it's version 102) they started (Google, as 'Chrome' is now base for Chrome, Opera, Firefox and some other browsers.) to block GPU rasterization for AMD APU, for some claimed performance bug. That's disputable by itself but even worse, there's CPU block list, if you have it you are out of luck, even if everywhere it shows that you have it enabled. To make things worse it's doesnt even matter if you use the APU or if you have dedicated GPU.
Check all these that they are enabled:
Settings > Advanced
Use hardware acceleration when available: Enabled
Search for: GPU
Out-of-process SW H.264 decoding: Enabled (#platform-h264-decoder-in-gpu)
Override software rendering list: Enabled (#ignore-gpu-blocklist)
GPU rasterization: Enabled (#enable-gpu-rasterization)
Choose ANGLE graphics backend: D3D11 (#use-angle)
Note: D3D11D12 should also work, considering that you have it properly installed.
Search for: Vulkan
Vulkan: Enabled (#enable-vulkan)
Opera CPU consumption is back below 20%, overall CPU consumption below 60%, GPU used around 35%. Exact numbers depends on the charakteristics of the video. Without fix overall CPU consumption was 100%.
What I tried as the first didn't worked in my case but you are welcome to try it anyway. Go to bios and disable integrated GPU. In my case the effect was zero but maybe.. (because this is, how it supposed to work.)
It's possible that problem might not affect you, if you have dedicated GPU card from nVidia. I would almost bet on it. As this set up is more frequent, than mine.