@littleden Chromecast certainly an option for you. You may also wish to consider screen mirroring viaSmart Things which is recommended for Tvs from 2016 onwards https://www.samsung.com/uk/support/tv-audio-video/what-is-screen-mirroring-and-how-do-i-use-it-with-... If older Tv can use Smart View but from 5 October will no longer be able to download the app and support will cease. Should still work for customers who have it though.
Required a USB 3.0 Port. A21 simply doesn't support it. Even S10 lite has a usb 2.1. only devices to support this HDMI casting ability are:
Galaxy S8 and above
Galaxy Note 8 and above
Galaxy A90 5G