What if you add the subcategories links in the modal or with the new topic link?
For example:
Please choose a subcategory below to create a new topic.
<a href="/new-topic?category=parent/subcategory1">Subcategory1</a>
<a href="/new-topic?category=parent/subcategory2">Subcategory2</a>
<a href="/new-topic?category=parent/subcategory3">Subcategory3</a>
And you can modify the button with css. Like this
#create-topic {
&.btn[disabled]:not(.is-loading),
&.btn.disabled:not(.is-loading) {
opacity: 1;
cursor: pointer;
&:hover,
&:focus {
background: var(--primary-medium);
color: var(--secondary);
svg {
color: var(--secondary);
}
}
}
}