Variable option disappears when inside Main Component

I’ve created a main component button that allows me to add a variable when used in a frame of its own.

But when the same child is placed within another main component, the variable option does not appear.

I’ve tried recreating the component from scratch but the result is the same. I’ve also tried applying the variable and then pasting it into another component but the variable also disappears. Is anyone else experiencing this issue where the variable option is not available or disappears?

It seems variables are not supported for nested components, according to Variant binding for component's instances