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.
Defeated the Titan and completed the main story on Ares Island.
Gathered 200 Koco.
Landed all catches at one fishing spot.
Completed the fishing tutorial.
Defeated the Titan and completed the main story on Kronos Island.
Earned 100 Purple Coins.
Encountered a starfall for the first time.
Repaired all Portals on Kronos Island.
Performed a Phantom Rush for the first time, outside of the training simulator.
Spoke with Elder Koco for the first time.
Destroyed 100 breakable objects.
Spoke with Hermit Koco for the first time.
Completed the Kronos Island tutorials.
Activated a Power Boost for the first time.
Defeated a guardian 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.
Defeated the Titan and completed the main story on Chaos Island.
Defeated the Titan and completed the main story on Ouranos Island.
Defeated the final threat and completed the main story.
Viewed all Side Stories on Kronos Island.
Viewed all Side Stories on Ares Island.
Viewed all Side Stories on Chaos Island.
Viewed all Side Stories on Ouranos Island.
Viewed all Side Stories.
Completed all Challenges on Kronos Island and fully revealed the map.
Completed all Challenges on Ares Island and fully revealed the map.
Completed all Challenges on Chaos Island and fully revealed the map.
Completed all Challenges on Ouranos Island and fully revealed the map.
Unlocked all Skills.
Performed Phantom Rush 50 times, outside of the training simulator.
Raised Power Level to MAX.
Raised Defense Level to MAX.
Raised Ring Level to MAX.
Raised Speed Level to MAX.
Defeated all enemy types.
Defeated all guardian types.
Repaired all Portals on Ares Island.
Repaired all Portals on Chaos Island.
Repaired all Portals on Ouranos Island.