I’ll start talking about the story.

After the explosion of Titanic Monarch Eggman has already begun his new plan to invent his new invention. the time diamonds, using all the diamonds Eggman gains the power to travel through time
Thus destroying the past and impacting on the future
It’s Sonic’s goal to pick up these diamonds and change the past.
But the world was completely chaotic and it was almost impossible to reverse the situation but Sonic and his friends and shadow with their control of chaos will also help