Hello gtg500g,
Thank you for using Apple Support Communities!
We understand from your post that you would like to know if on-device dictation is the default and not a setting selection. That is correct, you do not need to enable the feature as it is already in place as described below:
Use Dictation on your iPhone, iPad, or iPod touch - Apple Support
"On iPhone 6s or later, and iPad, you can use dictation without being connected to the Internet. Earlier models of iPhone and iPad require an Internet connection.1
- Not all languages are supported by offline dictation."
Best Regards.