I have a requirement to hide the Manage section from the side navbar for the admin of the specific realm (but not the Keycloak admin user) and also make few changes in the Realm settings page as well.
how to customise the admin UI, how to build it to ?
It’s (nearly) impossibly difficult. Once upon a time, the Keycloak Admin UI (version 1, built in angular) was meant for customization, and doing so was fairly easy. It’s now a monolithic React app that changes radically with every release. Even if you achieve your relatively simple goal, get ready for it not to work every time a major version release is made.
No. If you have tried something and faced an error you can’t overcome, post a comprehensive description of what you tried and what error you encountered. Then maybe someone can help you here.