Nothing of considerable substance: https://www.moddb.com/games/manhunt/mods

You can find many mods for manhunt 1-2 here. Beginning from character skins, retextures, and ending with separate custom games and levels - https://www.dixmor-hospital.com/

You can also find them on these 2 sites, but there aren’t much of them. I would still suggest to use the Dixmor site. Cause there is a great variety of them.

https://gamebanana.com/mods/games/5330

https://www.nexusmods.com/manhunt

there are many but i can cite a few

blooddance (mod that re-implements many beta ideas into the game):
https://www.dixmor-hospital.com/mods/view/blood-dance-beta

binbag's toxic tide of terror (a whole new level):
https://www.dixmor-hospital.com/mods/view/binbag-s-toxic-tide-of-terror

HD mod:
https://www.dixmor-hospital.com/mods/view/manhunt-remastered