Strangely enough, 1 Sweet and 1 Sour is the only Herba Mystica combination that doesn't work with ANY typing as of January 2023, when this answer is being written. Every other combination will work with ground and steel, so no worries there. There are two other combinations that don't work with certain types, which are included in my source below. I'm hoping that this gets patched in the future, but for now you'll unfortunately need to find a third Herba Mystica. I wish you luck, as I haven't been too lucky with my Herba Mystica drops.
..or you could just find someone who's willing to make the sandwich for you via Union Circle that would work too as long as you both are involved in the sandwich-making process.
Source for the Herba Mystica combinations.
Source for the multiplayer sandwich segment.
