ACF Frontend – Mandatory Taxonomie?

I have created a form where users can submit files (posts) for my website.
They also need to choose a post category (taxonomie).
All post categories are subcategories of the category “Lyrics”.
How can I make that the Category “Lyrics” is always checked (and can’t be unchecked) and they only choose from one of the subcategories?

And how can I limit to only one selection?

Thanks in advance!