Don't want to write this by hand? GodCraft sets minecraft:interact_button for you with a switch.Get GodCraftOverview
minecraft:interact_button is an item component: it goes in the components object of a custom item. Shows an action button on touch screens while the item is held. Set it to true for the standard "Use Item" label, or give a text to show your own label.
Example
Inside the components object of BP/items/<name>.json (values are the defaults or placeholders):
BP/items/<name>.json
{
"minecraft:interact_button": true
}