I'm a modpack dev. I've been studying the wiki and I really have found no way to simply add a recipe. I haven't made a modpack since 1.8 so I'm used to JEI and Crafttweaker and don't really know how to edit data packs or resource packs.
For example, I want to test it out by adding a world interaction recipe for basalt. How would I go about doing that?

EMI is just a 'recipe' viewer just like JEI so it can't add recipes itself. So if you want to simply add recipe you can use kubejs and CobbleGen or just using vanilla datapacks which has tutorials on the Fandom Minecraft Wiki.

I might add support for world interaction recipes to be resource packed into the game, it could be useful for modpack devs. However, the basalt recipe should be in vanilla, so I've added it and will be released in the next update.