A "hunger in Peaceful" mod. Disables passive health and saturation regen and enables Easy-difficulty hunger decay on Peaceful. Does not update the corresponding settings menu tooltip, because I am lazy. Does not require the Fabric API.
I mostly made this because none of the existing mods had been updated to 1.21 and I wanted to play it myself
There are a few other mods like this one. This mod in particular was inspired by the mod Hunger on Peaceful and techguy16's fork for 1.20. The latter has now also been ported to 1.21.4 if you'd prefer to use his instead.