Checkboxes can never be made mandatory in Salesforce, either at field level or at page layout level. Being a Boolean field, the default value is always set to “False” for a checkbox field.
In the below screenshot, a new custom field named ‘Is Active’ is created on Account, as it can be seen the default value is already set to “Unchecked” or “False” and there is no option to mark this field either as Required at field level or at page layout level.
Refer attached screenshots for details:
