Hi,

Yes, you can prepare for NMAT 2021 from Arun Sharma's books as those are very good for clearing your concepts and strengthening your basics. However, in order to prepare yourself for the NMAT examination you should focus on the mock tests which are available online. Those help you know better about how much you've prepared so far and they also provide an idea about the level of testing and the type of questions for the NMAT exam.

I hope this helps,

All the best.