iOS 18 - new Notes App function - collapsable sections

If I have converted a text part into a heading, the entire text that follows ends up in the collapsable section. It is not possible to select only a few lines of the following text for the collapsable section. It is also not possible to write additional text outside the section, i.e. behind the section, in a new line, which has nothing to do with this section, and will not collapse. Either this is a big bug or I am too stupid to understand how this works. Unfortunately, I can't find any help that explains this.

Thanks in advance if anyone knows how to do this!