Amazon.com: Samsung 256GB Micro SDXC EVO Plus Memory Card with Adapter Works with Samsung Galaxy S7, Tab S7+ Tablet, A21s Smartphone (MB-MC256KA) Bundle with (1) Everything But Stromboli SD, TF Card Reader :
clear cashe for A21s - Samsung Community
How to Insert Sim cart| SD cart in Samsung Galaxy A21S |Memory card slots |MicroSD card| Nano SIM - YouTube