Gunk definately won’t help with this. Best thing to use would be a cotton bud and some cleaning alcohol / isopropyl alcohol, and plenty of time and patience. If it’s a desktop keyboard you can maybe pull the keys for cleaning after taking a picture of the layout so you can put them back but for laptop keyboards they can be a bit fragile so not worth pulling the keys
Also some compressed air would be great for getting rid of any crumbs sitting under the key. Have you spilled any drinks on it or anything?