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.
Completed all Challenges on Ares Island and fully revealed the map.
Repaired all Portals on Ares Island.
Landed all catches at one fishing spot.
Repaired all Portals on Kronos Island.
Defeated the Titan and completed the main story on Kronos Island.
Completed all Challenges on Kronos Island and fully revealed the map.
Viewed all Side Stories on Kronos Island.
Gathered 200 Koco.
Earned 100 Purple Coins.
Encountered a starfall for the first time.
Completed all Missions in one Cyber Space area.
Completed the fishing tutorial.
Spoke with Elder Koco for the first time.
Destroyed 100 breakable objects.
Performed a Phantom Rush for the first time, outside of the training simulator.
Spoke with Hermit Koco for the first time.
Achieved Rank S time, for the first time in a Cyber Space area.
Activated a Power Boost for the first time.
Completed the Kronos Island tutorials.
Defeated a guardian for the first time.
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 Ares Island.
Viewed all Side Stories on Chaos Island.
Viewed all Side Stories on Ouranos Island.
Viewed all Side Stories.
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 Chaos Island.
Repaired all Portals on Ouranos Island.