Bug #92732
Updated by Daniel Siepmann over 3 years ago
https://docs.typo3.org/c/typo3/cms-core/master/en-us/Changelog/10.3/Feature-90266-Fluid-basedTemplatedEmails.html states `setFormat` should be used, while `format` is implemented.
See implementation:
https://github.com/TYPO3/TYPO3.CMS/blob/10.4/typo3/sysext/core/Classes/Mail/FluidEmail.php#L70
https://github.com/TYPO3/TYPO3.CMS/blob/master/typo3/sysext/core/Classes/Mail/FluidEmail.php#L70