Yeah, seems it was removed from the xml in A21. Here is the xml for it from A20:
<item_modifier name="modGunMeleeBlessedMetal" installable_tags="weapon,tool" modifier_tags="specialDamage" blocked_tags="noMods" type="attachment">
<property name="Extends" value="modGeneralMaster"/>
<property name="UnlockedBy" value="modGunMeleeBlessedMetalSchematic"/>
<!--Do double damage to evil / undead-->
<effect_group tiered="false">
<requirement name="EntityTagCompare" target="other" tags="zombie"/>
<passive_effect name="EntityDamage" operation="perc_add" value="1"/>
</effect_group>
</item_modifier>
And the icon, in case you wanna add it back in.
View attachment 30217