Dear Team!
I had already fixed this problem. Opera has two '.exe' files, 'launcher.exe' and 'opera.exe' to run it, we must add 'opera.exe' to 'Graphics settings' of window 10 to enable using dGPU in Opera. If we add 'launcher.exe' to 'Graphics settings', it will not work.
To find location of 'opera.exe' file, you can use search function of window in C drive.
Thank all for your support!