TYPO3 Core

Currently, via form definition files, it is only possible to set additionalParams.
Adding additionalAttributes is only possible, if you override the Form.html with your own Extension.

So this should be possible:

TYPO3:
  CMS:
    Form:
      prototypes:
        standard:
          formElementsDefinition:
            Form:
              renderingOptions:
                additionalAttributes:
                  novalidate: 'novalidate'

If you add

additionalAttributes="{form.renderingOptions.additionalAttributes}" 

to the typo3/sysext/form/Resources/Private/Frontend/Templates/Form.html