They haven't updated the a51 5g past that. IDK why, but even phones like the a01 have. There isn't anything I can help you or me with regarding this but there isn't any firmware past October 2020 for the sm-a516b so you can't even flash a newer one if you knew how to.
the thing that annoys is the cheaper A series phones are on more upto date software after paying £430 for this phone I thought we would be in front and not behind but there's nothing we can thanks for all the help.
Its a little annoying tho. Samsung Galaxy A51 5g is one of Samsungs best midrange phone if not the best and yet Samsung aren't giving it very many updates. I also have that phone. Tbh Im just happy that I have no probelms which desperately need to be fixed by an update. All is flawless on my phone at the moment 😊