Currently, setting the default value for a single-select column type can be achieved either when creating the column type, or by customising the column type after it has been created.
Feature request:
Implement a feature whereby the user can set the default value for the single-select column type in the ‘Edit single select’ pop-up.
More specifically, once the select options have been created, or when creating the options, there could be a checkbox (or another graphical widget) that appears next to the delete icon – which appears when the user hovers over an option – allowing the user to set one of the options as the default value.