Command for an enchanted item is the same as /give? i'm trying it but doesn't work.
'offhand' : '{Count:1b,id:"minecraft:stone_axe{Enchantments:[{id:"minecraft:efficiency",lvl:2},{id:"minecraft:sharpness",lvl:2},{id:"minecraft:unbreaking",lvl:2}]} 1",tag:{Damage:0}}',

Minecraft version: 1.19.2
Modloader: Forge
Forge version: latest
Environment: Singleplayer

Mod name: Starter Kit
Mod version: latest

I recommend using the /starterkit set command that will copy all enchants over correctly to the config file :)