Bone meal can be used on saplings that are on moss blocks, but they cannot grow into trees.
To reproduce
Place an oak sapling on a moss block
Use bone meal on it
→ ❌ The sapling gives off particles but it does not grow into a tree.
Linked issues
is duplicated by 1
relates to 7
MC-212226
Bone Meal can still be used on a Glow Lichen when it is unable to grow
Resolved
MC-224862
Azalea and Flowering Azaleas can take bone meal despite being on clay
Resolved
MC-15091
Bone meal is still consumed when the mushroom is in a position where it cannot grow
Reopened
MC-125642
Bone meal is consumed when used on fern, grass and seagrass even if it cannot grow
Resolved
MC-127995
You can use bone meal on sea pickles in situations where no sea pickles will grow
Resolved
2 more links
Can confirm in 21w05a.