Hi

RT stands for repeat theory. According to the circular released by CBSE in August 2021 among the eligible students for the compartment exam are

"After the declaration of results, students who are not able to meet the qualifying criteria in one subject and placed in compartment category."

Though this was for students appearing first time you will still have to go for compartment exam according to their circular

So if your previous result was better stick to it if you are unwilling to waste another year as compartment exams are conducted to save a students year.

You can check the circulars here

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.india.com/wp-content/uploads/2021/08/CBSE-2.pdf&ved=2ahUKEwjp6NGcjafzAhUJT30KHboOCRMQFnoECDMQAQ&usg=AOvVaw3tFEQi_cLHY7JHlUFjezgI

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.cbse.gov.in/cbsenew/documents/20210810_CIRCULAR%2520COMPTT%2520EXAMS%2520REGULAR%2520CANDIDATES%25202021_eng.pdf&ved=2ahUKEwjp6NGcjafzAhUJT30KHboOCRMQFnoECAsQAQ&usg=AOvVaw078ICpuY68IrMeS58Nybdn

https://news.careers360.com/cbse-hold-class-12-compartment-and-improvement-exam-2021-from-august-16

Hope this helps!