As the title says, shooting an arrow and getting it's onground tag returns false even though its on the ground.
To reproduce:
Shoot some arrows, then run /execute as @e[type=arrow ] run data get entity @s OnGround, it will say 0b always.
Expected result:
It will show 1b when it is on the ground and 0b while it is in the air.
Arrows use inGround; OnGround if for entities that fall when in the air; arrow physics are different and fall, as long as it's not in a block, as such, OnGround is never set/used (it's only part of the data, as it's part of the root entity data).