custom_mc_advancements/data/canopy/advancements/enter_the_void.json

{
	"display": {
		"icon": {
			"item": "minecraft:black_concrete"
		},
		"title": "Enter The Void",
		"description": "At least this only exists in the end... right?",
		"frame": "task",
		"announce_to_chat": true
	},
	"parent": "canopy:end",
	"criteria": {
		"below_-65y": {
			"trigger": "minecraft:location",
			"conditions": {
				"player": [{
						"condition": "minecraft:entity_properties",
						"entity": "this",
						"predicate": {
							"location": {
								"dimension": "minecraft:the_end",
								"position": {
									"y": {
										"max": -65.0
									}
								}
							}
						}
					},
					{
						"condition": "minecraft:inverted",
						"term": {
							"condition": "minecraft:entity_properties",
							"entity": "this",
							"predicate": {
								"type_specific": {
									"type": "player",
									"gamemode": "spectator"
								}
							}
						}
					}
				]
			}
		}
	}
}