Can lifting weights and intensity workouts lead to cardiac arrest and death? will it increase the thickness of the walls of the heart? i'm worried? i'm a 20 year old boy and i'm doing exercises in gym for 4 years.im worried?

It is very very unlikely that you will have ill effects from exercise. Just do not over do it. Moderate intensity workout will provide all the benefit you need. For healthy diet: http://www.choosemyplate.gov/. drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV and Covid vaccines. Wish you good health!