It seems that ammunition breakage is baked in to ammunition recovery after a fight, and that an unbreakable arrow would improve the recovery rate somehow, but RAW is RAW.
Assuming an unbreakable arrow is no more recoverable than an ordinary one, are there any benefits to having and using unbreakable arrows outside of very niche roleplay situations where someone tries to steal and break your arrows?
Unbreakable arrows allow for inventive puzzle solving
By virtue of the fact they cannot be broken outside of an anti-magic field, they lend themselves to a variety of inventive uses during exploration. For example:
shooting them into a vertical wall to make a stairs out of arrows
jamming up the gears in a mechanism (eg a complex trap)
a makeshift set of picks for use when climbing
stuck between some crushing walls? A few unbreakable arrows will stop those walls from killing you