I first thought no one has an issue with this setting not being in the game, only me (because i always toggle it and its possible in most games nowadays), but when i searched on if its the case i found a bunch of people have been requesting it as well, for a long time and still.
https://discussions.ubisoft.com/topic/77788/hold-to-sprint-option?lang=en-US
Have no idea why this option is not in the game but its for sure, feels bad. Please add this option before the games support ends.