I think the base game goes up to 3x3, whereas normally you'd register a craft recipe using minetest.register_craft:
https://rubenwardy.com/minetest_modding_book/en/items/nodes_items_crafting.html#crafting

For 4x4, you'll have to instead make a workbench with it's own separate craft system. Register a craft recipe to make the custom workbench (would have to be within 3x3), and then for that custom node, have it spawn a form on right-click, and probably use your own logic to scan and see if what's on the table matches a recipe, and so on. I'm sure it's something that'll probably be at minimum like 150 lines or so, just for a separate custom recipe system.

There's the source code for the MineClone 'crafting bench' for a starting point:
https://git.minetest.land/MineClone5/MineClone5/src/branch/master/mods/ITEMS/mcl_crafting_table/init.lua

As an aside, there is also a Minetest announcements account on fedi:
https://fosstodon.org/users/Minetest