This page of Assassin's Creed Valhalla's game guide answers the question if you can produce arrows. You will also find out what are the main methods of obtaining arrows across the in-game world.
Let's start with the information that, by default, Eivor can carry a very limited number of arrows in the quiver. You can change this by improving the quiver from the inventory level. You have to spend crafting materials for this. The first upgrades are quite cheap. For example, the first quiver upgrade requires only 30 pieces of leather and 20 iron ores.
Unfortunately, Eivor cannot produce arrows on his/her own and as a result, you have to rely on the arrows found in the game world.
Look primarily for racks and different kinds of shields, which have a lot of arrows sticking out of them. It is also worth examining the corpses of defeated opponents and wildlife. If the arrow you used to attack a given enemy did not break, you can pick it up and use it again.
If you run out of arrows, you can also:
- Switch bows. There are three types of arrows in the game that match three different types of bows - light bow, hunter bow, and predator bow.
- Visit any merchant in the game world (it can also be the one from the Viking settlement). They sell all three types of arrows - they cost from 1 to 3 silver per piece.