Nobody replay so I reply myself maybe it will be helpful for somebody
Today I reset Opera settings and after that automatic switching accordingly macOS setting started working but in my opinion it is Opera error.
If I just one time manually switch Opera theme in Opera settings it broke automatic switching according to macOS setting. I can not find settings responsible for this in Opera menu. Only way is to reset Opera settings.
Hope it will be solved in next releases.
Best regards
Arek