I'll look into the Samsung backup - didn't know that existed...
Without resetting my phone again, unless there is a way to delete the messages currently on my phone or find an app that will overwrite the existing data, I believe it is something inherent in the S21...
Actually, it doesn't exist... I'm on Verizon and Samsung cloud is unavailable. And I've already tried multiple variations in smart switch.
But that also seems exactly the same as using Google drive or Dropbox, both of which I've done using SMS backup and restore
Unfortunately, Google backup is only available when you first set up your phone. And you can't access pieces of it