You can use headlines for structuring the registration form (see image 1 as an example).
Please go to:
Overview => Settings => Manage Participant Groups
First, turn on the Expert Settings toggle in the lower navigation bar.
The toggle is labeled "Expert Settings Disabled" until activated.
This gives you additional options for editing the participant groups.
You can use the field "Prefix Text" to add headlines above the different participant groups (see image 2). This could give more structure to the presentation of the different participant groups.
To make the prefix text stand out, you can use <h3> to show it in bigger font and a separate line, for example <h3>Participants from Low GDP Countries</h3>.