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)"
Check with your supplier. There are different models for different countries. I think for Nordic all models is dual sim THAT is 2 physical nano sim cards or 1 nano sim and 1e-sim.
Looking at all the tech sites like sammobile and Samsungs own technical site the Samsung Galaxy s21 Ultra is Dual Sim @Scotcruz in the UK.
On a side note It does not however support a sd card anymore.
Current Phone > Samsung Z Fold³ 5G.