It was just a matter of time. There have been two decades of mods for the original Diablo 2 and many reasons to tinker with Diablo 2: Resurrected beyond the graphic overhaul and shared inventory. The mods that are popping up on NexusMods and ModDB are undoubtedly just the beginning.
There are difficulty adjustments like Enemy Multiplier, which allows you to double up to ten times the number of monsters, and Lower Resist, which replaces elemental immunities with resistances during nightmare and hell difficulties. D2R Drop Mod and Guaranteed Drop Mod both have you messing up with drop rates. The former increases the likelihood of getting good loot from tough enemies, while the latter simply makes every single enemy drop something. Splash damage in close combat causes nearby enemies to take half the damage you deal. Hide your helmet, well, it hides your helmet.
Better SP is full of quality of life improvements, such as increased inventory and hiding size, faster walking and running (and less stamina loss), higher stacking limits for arrows, bolts, keys and tomes, higher mana regeneration, Horadric Cube recipes for Respec tokens and removing Items without losing gems, higher maximum skill levels, changes to the secret cow level and more. Sounds great – if someone could just modify a decent modern hotbar to use your skills.
Note that most of these mods warn that they are intended for offline single player gaming and that if you get banned from using them it will be hard cookies.