Resign without Offer Letter

Hi all, I am working as a java production support engineer for 4 years in a BFSI project.This is my first and it is legacy project with no growth and toxic environment. Im just doing some incidents and minor code changes. I feel there is no growth and theres is no recognition for the work which I’m doing. Im trying to up-skill on spring and spring boot role, but not able to focus much. I want to resign first by this month end and then plan to prepare and apply for jobs in the next 90 days notice period. Is it a good option. Please advice.