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