Single choice questions and multiple choice questions are different in terms of logic and operation. Therefore, most operating systems use a different representation. In Windows, for example, these are circles (radio button) and boxes (checkbox).
If you use the default layout, SoSci Survey uses the input elements of the browser, which in turn follows the representation of the operating system. This has the advantage that the users can see what they have in front of them based on the display and this in turn is important for intuitive operation.
If you question this quite reasonable interaction, SoSci Survey of course also offers you the possibility to use your own controls. Some variants such as “circles with crosses” or “boxes with check marks” (without differentiation according to the type of selection question) can be selected in the Questionnaire Layout. If you have even more specific ideas, you can also design your own Input Elements.