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