I am not entirely sure if this was an intended feature, but in the typography heading settings, if you put a clamp function in the font size, sometimes it works and sometimes it doesn’t. This seems to be different between sites and there doesn’t seem to be a reason why it would work in one and fail in another. It also may work in an h2, but not the h1. Since this is a valid CSS unit, it should work. It does seem to do better if you create a custom typography setting and then apply its size to the heading level, but that seems like a lot of custom settings and unnecessary variables for just a font size.