Scaling Health

Scaling Health balances difficulty by letting players, mobs or both gain extra health - or lets players start with fewer hearts. A per-player difficulty value rises over time and makes mobs stronger, while heart crystals raise a player's max health.

It is highly configurable (datapacks included), needs Silent Lib and runs on Forge for Minecraft 1.14.4 - 1.20.1. For 1.21+ the author points to Silent's Power Scale.

Its difficulty system is server-friendly, so it fits a modpack on Minecraft hosting; install it with one click in the panel.