Here are the important topis with its Weightage of JEE Main:

Physics

Mechanics- 30%

Heat & Thermodynamics -7%

Electrostatics & Current Electricity- 17%

Magnetics & Electro Magnetic Induction- 13%

Optics & Waves- 3%

Modern Physics- 10%

Simple Harmonic Motion, Waves & Elasticity- 7%

Semi-Conductor Devices, Electromagnetic Waves and Principles of Communication- 13%

Chemistry

Organic Chemistry- 30%

Inorganic Chemistry- 30%

Physical Chemistry- 40%

Mathematics

Co-Ordinate Geometry- 17%

Calculus- 27%

Algebra- 27%

Vector/3-D Geometry- 10%

Trigonometry- 6%

Sets & Relations, Mathematical Reasoning, Statistics- 13%

You can also refer below given link for the further information.

https://engineering.careers360.com/articles/jee-main-syllabus-weightage

Good Luck!