The Hidden Ones DLC adds more upgrade slots to the ones listed below. The 10's get 2 more. The 5's get 1 more. This brings the total upgrade slots to 60, but you still only need 20 for this achievement.
There are 6 items you'll be wearing that benefit from 50 total crafting upgrades. If you care about making Bayek buff, you'll go way past the 20 upgrades for this achievement. There is a Ubisoft Club badge and a Ubisoft Challenge for maxing your upgrades.
Hidden Blade* - 10 - increased hidden blade damage
Quiver - 5 - increased arrow capacity
Stabilizer Glove - 10 - increased ranged damage
Bracer -10 - increased melee damage
Breastplate - 10 - increased health
Tool Pouch* - 5 - increased tool capacity
* you get the tool pouch and hidden blade separately after some story progression
You'll need to gather crafting materials to be able to perform such upgrades. These are received from hunting animals, dismantling weapons, looting corpses and containers, buying from nomads, completing quests, etc:
Cedarwood
Bronze
Iron
Soft Leather
Hard Leather
Pelt
Carbon Crystal
Silica - this is listed as a crafting material, but you'll need these for activating the 6 Ancient Mechanisms in as many tombs. 75 total silica are needed for all 6 mechanisms. There are at least 90 total silica in the game to find; mostly in tombs and special places.
Sometimes, you'll notice a notification that crafting is available on an item. Or you'll just see an available upgrade in the Gear tab of the Character menu. In the bottom half of the Gear screen, there are 6 icons with "Crafting" under them, 3 on each side of Bayek. If any of these icons has a small orange circle with a black !-mark in its upper left corner, then it can be upgraded. Hover over that icon and HOLD
to craft the upgrade. There is a meter on the right side of each crafting icon that shows the upgrade's level.
Craft 20 total upgrades over time, and the achievement is yours.
Housin 2203's
Solution for Handy Man In Assassin's Creed Origins adds a little info if you need help getting crafting materials.