Here is the full list of all 51 Red Dead Redemption 2 achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Red Dead Online: Reach Rank 50.
Red Dead Online: Concurrently own 5 horses.
Red Dead Online: Craft 25 pieces of ammunition.
Red Dead Online: Successfully counter a rival Posse's Free Roam mission.
Red Dead Online: Achieve MVP 3 times (in a round with at least 4 players).
Red Dead Online: Accept 10 Free Roam missions from characters around the world.
Red Dead Online: Purchase 5 camp improvements.
Red Dead Online: Form a Persistent Posse.
Red Dead Online: Complete a Free Roam mission as part of a Posse with at least 2 members.
Red Dead Online: Craft 20 items (excluding ammo).
Red Dead Online: Play 5 Free Roam Events.
Red Dead Online: Achieve 5 gold belt buckles from awards.
Red Dead Online: Reach Rank 10.
Red Dead Online: Sell 20 items to the Butcher.
Red Dead Online: Pick 25 Herbs.
Red Dead Online: Take part in a Series.
Red Dead Online: Complete the Intro.
Earn 70 Gold Medals in Story missions.
Skin every species of animal in Story Mode.
Study every animal across all states in Story Mode.
Find a permanent home for the squirrel statue.
Attain 100% completion.
Complete the Epilogue.
Complete 'A New Jerusalem'.
Find the graves of each of your fallen companions.
Complete 'Red Dead Redemption'.
Complete all optional Honor story missions.
Complete 'Goodbye, Dear Friend'.
Survive 18 bear attacks and kill the bear each time in Story Mode.
Discover the fate of Marko Dragic.
Reach maximum or minimum Honor level.
Complete Chapter 5.
Complete Chapter 4.
Complete 10 Stranger mission strands.
Complete one of the Collectable strands.
Spend $5000 across all shops.
Complete a Companion Activity in each camp.
Craft 30 unique items in Story Mode.
Survive 3 days holding a bounty of $250 in all states.
Play all mini games.
Complete Chapter 3.
Catch a fish weighing at least 16 lbs (7.3 kg).
Rob or loot $250.
Upgrade each available component for a single sidearm or longarm weapon.
Recover the stash from 4 homesteads.
Deliver 5 camp companion item requests.
Reach max bonding level with a horse.
Complete Chapter 2.
Donate $250 to the gang tithing box.
Complete Chapter 1.
Complete 'Enter, Pursued by a Memory'.