On sonic 06 how do you get rings after finished all of the missions?

You can't get rings after finishing all the missions in Sonic the Hedgehog (2006). Once you've completed the game, the ring count is essentially locked.

There's no way to collect more rings after the ending, and there are no hidden secrets or post-game areas to find them. This is because the game focuses on the story and doesn't include any additional gameplay elements after the final boss fight.

While you can't collect more rings, you can replay the game on different difficulty levels or try to achieve perfect scores on each level. This might reward you with an achievement or other unlockable content, depending on the platform you are playing on.