Here is the full list of all 18 Sonic Mania achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
That elusive perfect run, only a professional can achieve
Get through Stardust Speedway Zone as quickly as possible
Wreak havoc at the propaganda factory
Have your photos taken in Studiopolis Zone
Find the hidden item boxes at the end of the Zone
Collect all seven Chaos Emeralds
Gotta gacha 'em all
You might have to submerge to find it
We really like boats
Let the wind take you through
Collect gold medallions in Blue Spheres Bonus stage
Try for a 3 chain combo!
What would happen if you cross a bridge with a fire shield?
Achieve any ending
Collect silver medallions in Blue Spheres Bonus stage
Barrel through the lava, don't let anything stop you
Try pushing a barrel to see how far it goes
Spin the Star Post!