Just a thought, if you go to your SIM card settings, what network options are you seeing?
Ideally it will show 5g/4g/LTE/3g/2g (i.e. you should be able to access any of these whichever has the strongest signal at the time).
Is your signal usually good?
If both of the above are yes, and you've only had your device for a day, I would return it.
I am not employed by Samsung nor do I receive any remuneration as a Samsung Members Star.
My device is an S25 Ultra.