I have been observing from the past 10 days since I bought the mobile that Volte for both Sims sometimes work on Samsung M21 and sometimes not. The Volte symbol comes and goes on its own and there is nothing you can do about it.
I am using the same mobile network in my home on 2 mobiles: A Samsung M21 and a Redmi Y3 but Redmi Y3 never misses on Volte Signal while Samsung M21 for most of the time lacks Volte Signal.
I believe it is a Software glitch or Hardware issue with Samsung M21.
So I request other Samsung M21 users to kindly confirm if same thing happens with their Samsung M21 as well or is it a problem with my unit only.