Lots of new mobs - both hostile and passive. Using the mobs randomness mod you can create a datapack to alter the stats, equipment and other attributes of the mobs.
Tech mods - Mekanism + addons and Draconic evolution.
New world generation for all dimensions using mods like Better end, Incendium, Biomes O Plenty and more.
Over 200+ new ores in all dimensions.
Lots of quality of life improvements.
And much more to explore...
Only for version 1.20.1