Here is the full list of all 48 Sonic Forces achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Created your second Avatar
Restored peace to the world
Collected 10 Wispons
Completed 5 SOS Missions
Equipped a part in every slot
Defeated Infinite
Turned the tide of the conflict
Collected 100 parts
Drove off Infinite again
Completed your first SOS Mission
Utilized the Rental Avatar function
Defeated 1,000 enemies
Changed Wispons for the first time
Completed 3 Daily Missions
Liberated a world
Collected 50 parts
Drove off Eggman
Drove off Infinite
Defeated Zavok
Created an Avatar
Cleared Stage 1
Cleared all Secret Stages
Cleared all EX Stages
Collected all Red Star Rings
Collected Number Rings three times
Collected all Number Rings
Collected Silver Moon Rings three times
Collected all Silver Moon Rings
Collected a total of 10,000 rings. (All Rings held at the end of the stage will be counted.)
Collected a total of 50,000 rings. (All Rings held at the end of the stage will be counted.)
Collected a total of 100,000 rings. (All Rings held at the end of the stage will be counted.)
Defeated 5,000 enemies
Defeated 10,000 enemies
Used the Closet
Achieved a soldier's highest honor
Achieved highest honors with all races
Made it into the rankings
Collected 30 Wispons
Collected all Wispons
Collected 500 parts
Collected all parts
Completed 5 Daily Missions
Completed 10 Daily Missions
Completed 10 SOS Missions
Completed all Challenge Missions
Collected all Red Star Rings in Shadow's Story.
Collected all Number Rings in Shadow's Story.
Collected all Silver Moon Rings in Shadow's Story.