Hello student yes Electromagnetic is an important topic for Jee main entrance examination it's expected as per previous year records that at least one question every year from Electromagnetic wave topic.

Some of the most important Chapters are as mentioned below -

Rotational Motion

Thermodynamics

SHM

Electrostatics

Magnetism

Optics

Modern Physics

For more details refer to the link the link mentioned below *https://www.google.com/amp/s/engineering.careers360.com/articles/most-important-chapters-of-jee-main/amp

Feel free to comment if you've any doubt

Good luck

Hello

The electromagnetic wave topic is important for JEE main but not completely. There are some important formulae in the topic they are important. There are questions based on that formulae. But if you have done other topic perfect then you can skip this chapter. But in this case you should have to perfect in other topics so that you can solve problems on that topic and so that it will not affect on your marks if you skip electromagnetic wave chapter.

Hope my answer will help you

Thank you