How to make roguelike items

I’m trying to make a simple roguelike with items in the same vein as risk of rain or Rounds. How do I get this items that hold multipliers to change the stats of the player, enemies, and bullets? I was hoping to also do this in a similar manor to vampire survivors where you can click on a UMG widget to pass that specific items multipliers to the different actors as needed.

The “built in” way to do this in Unreal, is to use the Gameplay Ability System (GAS.)
It lets you define properties, multipliers, temporary and permanent buffs and debuffs, and much more.
Here’s a pretty good tutorial: