I think I understand. You have multiple parent/child hierarchies in Category and want them as separate dropdowns?

It is best not to do it this way. Instead you need to split the terms into at least two taxonomies. If, for example, you were doing locations, you might have Area (e.g. East Bay) and region (e.g. Alameda) or whatever name for the taxonomies that makes most sense.

You can use a plugin to add these custom Taxonomies, and another plugin to move the Category terms (always switch the parent of the children with the children).

This post tries to explain this a bit better (you can use a plugin to switch category terms from category to any new taxonomy that you make, so it is not so hard to do). It is a really awful preachy lecture I wrote:

https://support.searchandfilter.com/forums/topic/multiple-categories-combination/#post-55166

Sorry about the tone, but the message is right and it links to good plugins (except taxonomy switcher I think). If I missed anything (I probably did, my apologies), follow up and nudge me.

Hi,

I removed the unwanted parent-category via the custom CSS. For example when the site-ID of the parent is 74 then you could write in your custon CSS file something like this:

.sf-item-74 {
	display: none;
}

And if you want to remove the “All Categories” then you could write:

.sf-level-0.sf-item-0 {
	display: none;
}

Did I understand you right?

sorry, I’m not sure if I understand your question right.
Do you want that the dropdown has no value in the beginning?