Sub-categories first in Composer category selector

[Arkshine]

A quick CSS solution could be the following. Put it in your theme or a component CSS.
It reverses category → sub-category to sub-category → category:

// Reverses position from "category -> sub-category" to "sub-category -> category"
.select-kit .select-kit-row.category-row .category-status,
#reply-control .category-input .category-chooser .selected-name .name {
    flex-direction: row-reverse;
}

// Hides the parent category when a sub-category is selected
#reply-control .category-input .category-chooser .selected-name .name {
    & > .badge-category__wrapper:first-child {
        display: none;
    }

    & > .badge-category__wrapper:last-child {
        display: unset;
    }
}