If your question is if you can first take admission and then write NEET, the answer is NO. If you want to take admission in MBBS/BDS/ Ayush or Veterinary courses, you can take admission only based on your NEET score and nothing else. So you have to qualify and be eligible in NEET. You can take admission in the same year that you have appeared in NEET if it is in India. But if you want to study MBBS/BDS abroad, then your NEET score is valid for 3 years. NEET is a pre assessment exam and not a post assessment exam.  And to be eligible for NEET, you should have completed your 12th, passed in all subjects and secure a minimum aggregate of 50% in Physics, Chemistry and Biology. It is 50% for General Category, 45% for PWD and 40% for OBC,SC,ST. Now if you belong to OBC Category, the Category you belong to should be also listed in the Central OBC list. Or else you will be considered as General Category and so you have to secure a minimum aggregate of 50% in Physics, Chemistry and Biology. This 50% is inclusive of the Theory and Practical marks scored in Physics, Chemistry and Biology collectively. You needn't score 50% in Physics, 50% in Chemistry and 50% in Biology separately. You need an aggregate of 50% or 40% depending on your Category as an aggregate in Physics, Chemistry and Biology. And along with Physics, Chemistry and Biology, you should also have studied English as one of the core subjects in your 12th. But if your question is if you take admission in MBBS through NEET 2020 and still want to appear for NEET 2021, yes you can.

Hello aspirant!
Hope you are doing well!

Yes you can join any medical college and give examination NEET2021. But according to latest news the NEET2021 has been postponed. Refer to this article

https://news.careers360.com/neet-pg-2021-exam-postponed-until-further-notice

Also you need to prepare yourself with the updated course of NEET. The authorities will release the syllabus outline by first week of December
https://medicine.careers360.com/articles/neet-syllabus

You can also use careers360 articles to learn more tricks on solving NEET2021 easily
https://medicine.careers360.com/articles/neet-mistakes-you-must-avoid-on-exam-day