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