This exact item works in single player, and also works in realms with one exception. The eating animation only happens in single player worlds, once uploaded to realms the effects of eating the item still happen, but the game does not show any animation. Code is below

{
"format_version": "1.16.0",
"minecraft:item": {
"description":

{ "identifier": "us:binding_powder" }

,
"components": {
"minecraft:use_duration": 32,
"minecraft:food": {
"nutrition": 1,
"saturation_modifier": "poor",
"effects": [

{ "name": "fatal_poison", "chance": 0.7, "duration": 10 }

]
},
"minecraft:hand_equipped": true
}
}
}