There is a couple of interesting ways to organize something like this.
Use Tags as a Subcategory instead with a must use 1 tag.
Air Theme has a categoru grouping with Headers in the list.
Ie
Category Group Name Header 1
- listed Categories
My current setup is using a parent and sub. It does create some annoysnces at times especially as admin I can post anywhere lol.
In Parent I keep See permission with subs hsving full permission.
Category hider theme component works well to cleam up Hamburger so it only shows parent categories.