Health Overlay is a client side mod that replaces the default heart renderer which always added more rows when the player had more than 20 health. The health is now in the same row but just displays different colored hearts, it also does the same with absorption. If your maximal health is under 20 the mod also renders "empty" hearts.
This mod was made to work together with Stats Keeper, but can be standalone. You can probably already guess that this mod was inspired by Mantle which adds the same feature but its made for forge, I wanted something that works with Fabric!