This is still happening, I move a tab to another monitor, and even dragging it to the top of the screen, it does not maximize, it seems like it is but its not. It's absolutely annoying and needs a fix!
@Jesseab Opera using 70% CPU with just YouTube and Facebook open may be due to hardware acceleration, heavy extensions, or built-in features like VPN or crypto wallet. Try these quick fixes, I hope this will solve the problem.
Turn off hardware acceleration in Opera settings.
Disable unnecessary extensions at opera://extensions/.