The Bug:

minecraft.custom:minecraft.damage_dealt doesn't increase when the fire aspect or flame enchantment damages entities.

Steps to Reproduce:

• Create a scoreboard objective for tracking when you deal damage and set it to display on the sidebar.

/scoreboard objectives add DamageDealt minecraft.custom:minecraft.damage_dealt
/scoreboard objectives setdisplay sidebar DamageDealt

• Give yourself a sword enchanted with fire aspect or a bow enchanted with flame.

/give @s minecraft:wooden_sword{Enchantments:[{id:"fire_aspect",lvl:2}]}
/give @s minecraft:bow{Enchantments:[{id:"flame",lvl:1}]}

• Summon a husk.
• Damage it with your enchanted sword or bow.
• →  Notice how the scoreboard doesn't increase upon the fire aspect or flame enchantment damaging the husk.