There’s the normal join - ctrl+j, which is good when you work inside blender because its not permanent. Outside Blender (game engines for example) “join” is not always optimal because these programs or engines can see it for what it is - separate objects. I don’t want that because this separation leads to a problem (animation problem).
I know there’s a way because i did it several years ago, but can’t remember how or what the function is even called? Anyone know?