You can't select radio buttons because 'for' attribute on label tag is missing. If you go through generated html of below code there will be no 'for' attribute on label tag.
AccountsTemplates.addField({
_id: "fruit",
type: "radio",
displayName: "Preferred Fruit",
select: [
{
text: "Apple",
value: "aa",
}, {
text: "Banana",
value: "bb",
}, {
text: "Carrot",
value: "cc",
},
],
});