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