How many fingers are needed? How many fingers did itadori needed to consume in order for his soul to be controlled by sukuna who gave him a chance to live in one of the episodes.
Sukuna has 20 fingers. If Yuji were to eat all 20 fingers, then still Sukuna won't be unleashed (currenly there are 147 chapters in manga, so the reason is still yet to be known). Itadori can supress him, and the only way to unleash Sukuna for a little while would be to consume several fingers at once, but after a certain amount of time Itadori would take control again.
Currently Sukuna can only take control of Itadori’s body only for a minute (Sukuna calls it &quot;enchaning&quot;) and can't kill or hurt during that minute. It was a binding vow and Itadori doesn't remember he agreed to that and this option hasn’t been used.

 Currently, Yuji has consumed 15 fingers as of chapter 147

Sources (Warning: spoiler links):

https://www.quora.com/In-Jujutsu-Kaisen-if-Itadori-consumes-all-20-fingers-will-Sukuna-be-unleashed-having-taken-over-Itadori-s-body-completely
https://www.reddit.com/r/JuJutsuKaisen/comments/hk981f/sukunas_fingers_status/
https://jujutsu-kaisen.fandom.com/f/p/4400000000000023463