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