Don't want to write this by hand? GodCraft sets minecraft:display_name for you with a switch.Get GodCraftOverview
minecraft:display_name is a block component: it goes in the components object of a custom block. Sets the name players see for the block in the inventory and tooltip. Give a translation key from your .lang file so the name can change with the language, or plain text.
Example
Inside the components object of BP/blocks/<name>.json (values are the defaults or placeholders):
BP/blocks/<name>.json
{
"minecraft:display_name": {}
}