As per the documentation and as experienced myself it's only possible to update “Text” and "Picklist” fields through the Salesforce Docusign apps launcher / field updates section.
Whereas at the completion of an envelope I wanted to update a checkbox to false, it’is possible to find the field in the field update section and give value input (false), however field update rule this is not saved.
First of all I think when a field cannot be updated, it shouldn't be shown, but second and most important, it should definitely be possible to allow for updating simple fields like checkbox or number.
ps I had this checked with Docusign support Adeel