Have you checked that your SIM card works in another phone?
Have you correctly installed the 2 SIM cards as per page 21 of the Samsung User Manual? See screenshot...
I had the same issue with my sim slot 1 as it wasn't working no matter how many sim cards i try. So when i tried above mentioned trick by inserting a paper under the sim card then it started working.
Now i am afraid if it ever stopped working while in some emergency this would be a big issue as a customer point of view. Samsung has to come up with some permanent solution on this.
My phone is made in Veitnam and bought in April-2021.
Thanks to Jiggy1.
You are a saviour my friend. I hope these Samsung jokers read this post and fix the product quality. The sim tray ia faulty. I used 2 papers im Sim 1 and looks like its working.