@Jackson3: That's right, but don't worry. With 128Gb or 256GB of internal storage available on the S21, plus the wide range of cloud services available to you, you won't have to worry about running out of storage.
Sometimes change is hard and I submit one of the draws to a Samsung phone was expandable storage.
For me I've never chosen below 256gb which has always been ample.
Sd cards can fail or corrupt which is what happened to me which put me off from using another.
I now use Dropbox to automatically send every photo I take to provide a secondary back up.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
Actually according to gsmarena it has only place for 1 sim-card and en eSim so you can't have double nano-sim cards in it. If that's real I won't buy it unfortunately.
"Single SIM (Nano-SIM and/or eSIM) or Dual SIM (Nano-SIM and/or eSIM, dual stand-by)"