Here is the full list of all 40 Sonic Frontiers achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Viewed all Side Stories on Ouranos Island.
Viewed all Side Stories.
Defeated the final threat and completed the main story.
Defeated the Titan and completed the main story on Ouranos Island.
Raised Ring Level to MAX.
Performed Phantom Rush 50 times, outside of the training simulator.
Defeated all enemy types.
Defeated all guardian types.
Viewed all Side Stories on Chaos Island.
Unlocked all Skills.
Completed all Challenges on Ouranos Island and fully revealed the map.
Repaired all Portals on Ouranos Island.
Raised Defense Level to MAX.
Raised Power Level to MAX.
Raised Speed Level to MAX.
Landed all catches at one fishing spot.
Completed the fishing tutorial.
Defeated the Titan and completed the main story on Chaos Island.
Repaired all Portals on Chaos Island.
Completed all Challenges on Chaos Island and fully revealed the map.
Gathered 200 Koco.
Defeated the Titan and completed the main story on Ares Island.
Repaired all Portals on Ares Island.
Viewed all Side Stories on Ares Island.
Completed all Challenges on Ares Island and fully revealed the map.
Destroyed 100 breakable objects.
Viewed all Side Stories on Kronos Island.
Completed all Challenges on Kronos Island and fully revealed the map.
Repaired all Portals on Kronos Island.
Earned 100 Purple Coins.
Encountered a starfall for the first time.
Spoke with Elder Koco for the first time.
Defeated the Titan and completed the main story on Kronos Island.
Spoke with Hermit Koco for the first time.
Achieved Rank S time, for the first time in a Cyber Space area.
Completed all Missions in one Cyber Space area.
Completed the Kronos Island tutorials.
Performed a Phantom Rush for the first time, outside of the training simulator.
Activated a Power Boost for the first time.
Defeated a guardian for the first time.