Unlike with seeds, there are 11 items Draftout counts for this goal (pre 26.3):

• Oak Sapling

• Birch Sapling

• Acacia Sapling

• Dark Oak Sapling

• Spruce Sapling

• Jungle Sapling

• Cherry Sapling

• Pale Oak Sapling

• Mangrove Propagule 

• Azalea 

• Flowering Azalea

Items that do NOT count towards this goal are:

• Bamboo 

• Crimson, Warped, Brown or Red mushrooms

• Chorus Flowers

(General rule, it needs to be able to be grown into a tree, and nether trees are technically large mushrooms.)

Nearly all leaves will drop their respective sapling on a 5% chance when decaying or when mined. This means 1 in 20 leaves should drop a sapling, except jungle leaves, which drop 1 for every 40 leaves (2.5% chance), and mangrove leaves, which never drop a sapling.

Bear in mind when gathering jungle leaves that the ‘jungle bushes’ that generate on the floor of these biomes contain oak leaves, not jungle leaves. 

Wood hoes break leaves in 3 ticks, stone and copper hoes break leaves in 2 ticks. For instabreak, you need an iron hoe (or diamond, netherite or gold). 

Azalea trees can drop 2 different saplings — azalea leaves drop azalea (5%) and flowering azalea leaves drop flowering azalea (5%), though due to the low number of flowering azalea leaves per tree, you might need to dig down to the lush cave.

Mangrove propagules grow on the underside of mangrove leaves and always drop themselves if age 4 when mined. If you have 4 bone meal, you can bone meal a mangrove leaf and the hanging propagule to obtain it. Trial Chambers have a 66.67% chance to have an oak tree, mangrove tree or cactus in the entrance room.

The best biomes for different leaf types are:

• 3 — Dark Forest (dark oak, oak and birch)

• 2 — Forest (oak and birch)

• 2 — Lush Cave (azalea and flowering azalea)

• 2 — Jungle (oak and jungle)

• 2 —  Windswept Biomes (spruce and oak)

• 2 —  Savanna (oak and acacia)

• 2 — Meadow (oak and birch)

Loot

Plains village generic chest = 48.2% oak sapling 

Plains village weaponsmith chest = 22.9% oak sapling

Taiga house generic chest = 40.6% spruce sapling

Savanna house generic chest = 71.7% acacia sapling

The Wandering Trader has a 7% chance to sell each 8 of the generic saplings or a mangrove propagule for 5 emeralds each. The Wandering Trader can also sell moss blocks for 1 emerald at a 7% chance, making him a possible source for every single valid item for this goal. 

Moss

Bone mealing moss (NOT pale moss) will cause the moss to spread with a chance of generating an azalea and flowering azalea. See the following table from the Wiki below:

Shipwreck food chests have a 42.1% chance to have at least 1 moss block.

Trial chambers can generate moss blocks around a Slime Trial Spawner, as well as in loot from supply chests at a 20.4% chance per chest.

Otherwise, moss needs to be found in a lush cave biome.