I am going through documentations for project configuration in craftcms not sure what is the different between project-config/write and project-config/modify?
project-config/write takes the config currently stored in the database and writes it out as YAML files in the config/ folder. You usually don't need this since Craft does this automatically whenever you change something in the backend (unless you have turned that off).
project-config/rebuild attempts to rebuild the entire project-config based on the state of the entire database. This is only required in rare edge cases.
Rest you can check the official documentation here:
https://craftcms.com/docs/4.x/project-config.html#what-s-stored-in-project-config