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