When the title of a note extends past the double horizontal bars where the link to collapse the note is located, the collapse link can not be accessed. On iOS, there is a collapse link in the settings for each note, but not on Mac version. In order to collapse notes, I have needed to reduce the title to just a few words.
This is indeed a known issue, we’ll think about a solution. In the mean time you can instead use the Edit > Collapse menu item or it’s associated keyboard shortcut.