For most people, no meaningful effect — unless you have an actual biotin deficiency, which is rare. Biotin (vitamin B7) is important for hair health, but taking more of it than your body needs doesn't make hair grow faster or thicker.
Hair supplement marketing often overstates the science. If you're eating a generally balanced diet, you're unlikely to be deficient. Supplements may help in specific cases — pregnancy, certain restrictive diets, or diagnosed deficiencies — but they're not a substitute for treatments with stronger evidence behind them, like minoxidil or finasteride, for genetic hair loss.
If you suspect a nutritional deficiency is contributing to your hair loss, a blood test from your doctor is a better first step than guessing with supplements.