Dying Light 2 has an abundance of items and weapons around, but that is only because these items have limited durabilities that make them temporary items. However, a duplication glitch may allow you to keep your favorite weapon around forever,
To duplicate items in Dying Light 2, you will need to deposit items into your Stash during the Baba Yaga challenge. Doing so allows you to duplicate as many items as you want.
Here is a guide on how to duplicate items in Dying Light 2.
Alternate (No Hoverboard) Solo Duplication Glitch – Dying Light 2
Some caution should be taken as this method, as with other duplication methods, is prone to crashing the game. So backups and other safeguards should be prepared. This is just a more accessible duplication glitch as it does not require the Hoverboard but is still equally buggy.
Also take note that this method only works to duplicate consumables, accessories and weapons.

The first step is to head to the Baba Yaga Challenge.
It can be found at the tower with the crane right next to the VNC tower in the Garrison area. You can glide down to the crane from the VNC tower.

You will notice some mushrooms growing at the side of the crane’s powerbox. Interact with them to begin the Baba Yaga challenge.

You will spawn in the air on a flying broom. However, you do not need to participate in the timed course. Instead, you’d want to turn around and select an empty slot in your accessory wheel.
It is recommended to move quickly, as the longer you take your time, the higher the likelihood of a crash occurring.

Glide down onto a specific platform below that is part of a safe house. Go to the stash inside and deposit the item you want to duplicate. You can then proceed to cancel the challenge.
You will be teleported back on the crane, however you will notice that you are still equipped with the item you deposited.

You can now drop it as many times as you want, creating as many duplicates as you want.

Just remember to not be too greedy as the chance of crashes will increase the more you duplicate items, so probably a handful of copies is enough.
And if you need more, you can just perform the duplication glitch again.