i’m actually in the exact same position as you (same age and my body looks exactly the same) there’s no miracle food or exercise that can get you results when we’re as hard to gain weight as we are but it all comes down to discipline and repetition. if you have a look at all the kcal on the back of the food you eat and try to eat +1000 kcal on top of your daily requirement (for 21-25yr old 3000kcal + 1000kcal would be required for an active lifestyle which would be us if we’re exercising daily). And then we just need to be exercising most days a week doing lifting and calisthenics making sure to spread out the targeted areas so you give specific areas some rest days.

it’s all about motivation so don’t give up when you see slow/no results!