dnd 5e – How recoverable is magic ammunition?

The magic ammo is recoverable.

The weapon properties section of the player manual says that some ammunition can be recovered.

At the end of the battle, you can recover half of your expense
ammunition
taking a minute to search the battlefield. PHB.146

An archer must shoot at least one common arrow for each magic arrow if he intends to retrieve the magic arrow.

There are magic arrows that retain their magical properties after hitting a target, for example, the wonderful magical object "unbreakable arrow".

Looking for the arrows, first try to locate the magic. Then, feel free to give up looking for the other (s).

Example of smart and silly archers:

The smart archer shoots twice, shooting a beautifully magical and common crushing arrow.
Return bravely from the battle with the arrow (half of the ammo).

The silly archer shoots once, firing his precious arrow into battle. After searching, you are dismayed at not recovering anything.

Since this archer only fired an arrow, halving the ammunition results in half an arrow.

Whenever you divide a number in the game, round down if you finish
with a fraction, even if the fraction is half or more. (PHB
p.7)

The player when recovering ammunition will have to round the results. An archer looking for an arrow on the battlefield will not recover anything.