After adding Checked and Unchecked options to a custom checkbox field, wondering why the options aren't mutually exclusive, and posting that question to the Community (this post), I realized that the field should not have options. In a different app, checkboxes are binary fields, but I that is not the case in Jira.
I switched to a radio button, and added one option, so that the button behaves like a binary checkbox--IF I can hide the built-in None option. Can that be done?