These two cell phones are similar in many ways but also different in a few. You should have a look at this Samsung Galaxy A21 vs Samsung Galaxy A21s comparison before you make that purchase.
Samsung Galaxy A21
Samsung Galaxy A21 is a decent budget phone that matches price with performance (specs and price inside)
Samsung Galaxy A21 features a 6.55″ display, 32GB internal storage, 3GB RAM, 4000mAh battery. See full specs and price.