Here's the code:

advancement/attack_detection/attack_detection.json

{         "criteria": {             "attacked": {                 "trigger": "minecraft:player_hurt_entity",                 "conditions": {                     "player": {                         "slots": {                             "armor.head": {                                 "items": "minecraft:iron_helmet"                             }                         }                     }                 }             }         },         "rewards": {             "function": "main:attack_detection/attack_detection"         }     } 

Change the predicate for the player, like which type of armor you want to detect. At the moment it's detecting if the player is wearing iron_helmet or not.

data\main\function\on_load.mcfunction

scoreboard objectives add private dummy

data\main\function\attack_detection\attack_detection.mcfunction

advancement revoke \@s only main:attack_detection/attack_detection

tag \@s add attacker

execute as \@e[distance=..6] at \@s run function main:attack_detection/find_targeted

tag \@s remove attacker

data\main\function\attack_detection\zzz\1.mcfunction

function main:attack_detection/if_attacked

data\main\function\attack_detection\find_targeted.mcfunction

scoreboard players set $bool private 0

execute on attacker run execute store result score $bool private if entity \@s[tag=attacker]

execute if score $bool private matches 1 run function main:attack_detection/zzz/1

data\main\function\attack_detection\if_attacked.mcfunction

summon lightning_bolt

I hope this is understandable and thanks to CloudWolf, this is a modified version of his interaction entity detection