Hi there,
Hope you are doing well.
12k rank in OBC Category can be considered average and can fetch you some decent branches in decent NITs, IIITs and GFTIs. like:-
1) CSE:- IIIT Kalyani, IIIT Kurnool, IIIT Kottayam
2) IT:- IIIT Vadodara, IIIT Una
3) ECE:- NIT Mizoram, Nagaland, IIIT Sonepat
4) EEE:- NIT Mizoram
5) Mechanical:- IIIT Kurnool

Hope it would help.
Thank You.

Hello!
Here's a list of NITs and their opening and closing ranks for previous years, along with category specification:

https://engineering.careers360.com/articles/jee-main-cutoff-for-top-nits

These are for all the branches, so you can even have a look in accordance to your branch of choice!

Good luck!