Don't want to write this by hand? GodCraft sets minecraft:body_rotation_blocked for you with a switch.Get GodCraftOverview
minecraft:body_rotation_blocked is an entity component: it goes in the components object of a custom mob, or in one of its component groups. Stops the entity's body from turning to match the way it faces. Useful for mobs that should stay still, like a statue or turret.
Example
Inside the components object of BP/entities/<name>.json (values are the defaults or placeholders):
BP/entities/<name>.json
{
"minecraft:body_rotation_blocked": {}
}