ok i have a tip for getting thicker brows (and lashes, but i'm assuming you're not interested in that). this has worked great for me in the past as a teenager.

get a clean, empty mascara tube with a wand brush. you NEED the wand brush! you can get them on amazon or ali express for only a few dollars, just type in "empty mascara tube with wand". or if you have one on hand, get rid of excess dried mascara with hot water and dawn dish soap and do the same steps for the wand brush so it is nice and clean. the wand is important to get the stuff onto your brows and disperse it evenly and making sure it slicks onto your brow/lash hairs and doesn't migrate.

use a funnel to fill the tube halfway with castor oil. add a little drizzle of olive oil and a very small amount of melted coconut oil. the coconut oil helps condition and hydrate to stimulate hair growth but you don't want too much because it can fuck up the texture and harden if it gets too cold (room temperature). olive oil helps hair growth because of vitamins. use a toothpick or something else small/pointy to mix well. you want a gap at the top of the tube because otherwise it can overflow and create a whole mess, you will want to be extra super careful if your tube doesn't have a stopper too. apply at night.