@abusch is correct. There isn’t a simple on/off switch _in the way you imagine. This is because display of text, whilst enabled, was never an original feature of the map view design only being added to v4.0.0 (August 2007). then as now the rubric is:
The note text appears only if the note has text, the note is sufficiently large
IOW, the text is only displayed is there is enough room; for containers/agents this means the title bar is dragged big enough to see more of the title space and less of the viewport. There is no setting to auto-size notes so as to display $Text. Indeed, as the amount of text varies, how would the app judge.
Current behaviour is summarised in Notes displaying body text.
Thus text display is enabled if the user chooses to do so by altering the default note size. The implication is that you need to re-size your notes in order to show text. In toy screen grab , the top note isn’t showing text as there isn’t enough hight to fit in text. If you are wondering about the blank space between the title and text in the lower note icon it is the space reserved for a subtitle.
If you want all notes to start out much bigger so as to accommodate $Text, you could change the TBX document’s default values for $Height and $Width via the Document Inspector’s system tab. Note such changes are set a document level so each TBX would need customising separately.