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