With an AP EAMCET rank of 21,000 in the OC category, it is highly unlikely to get a CSE seat at SRM University AP. In previous years, the closing rank for CSE at SRM AP was generally below 4,000 for open category candidates. You may consider applying for other branches or explore CSE in mid-tier private colleges where the cutoff extends beyond 20,000.

With your AP EAPCET rank of 21,000 and OC (general) category, you have a good chance to get a seat in CSE at SRM University, AP. In previous years, SRM AP gave CSE seats even up to 35,000 rank in later rounds of counselling. Your rank is much better than that, so you can expect to get a seat, especially if you apply in early rounds and choose CSE as your top option.

You should register for AP EAPCET counselling, choose SRM AP CSE in your option entry, and keep checking seat allotment results in each round.

Here are websites where you can check more details:
https://www.careers360.com/university/srm-university-amaravati/cut-off