Bro bro I completed main quest 100% but hidden quest still 5 is there
It's right there in the name: hidden quest. It means that you have to go out and find them. Just keep interacting with everything and everybody you can and eventually you'll get them. (Yes, it can be frustrating at times. Join the club.)
This forum is also a good place to look for hints. Scroll down and read what others have had to say about it.