Can I swap my SIM between my two iPhones?

I have an old iPhone 5s and also a 2021 iPhone - I use the older phone as my everyday phone but when there are network issues I’d like to make wi-fi calls using the newer phone.

Can I simply swap the SIM from one phone to the other?

In theory and in principle I expect the answer to be ‘yes’ but a few years ago, when I was with ‘3’ and did a similar thing [between two android phones] they blocked the SIM, citing something about protecting me in case I’d had my phone stolen…… It caused me a lot of stress at the time as I was on a road trip and suddenly had lost my means of communication with friends and work…..

I’d like a definitive answer before I risk the same outcome.

Many thanks.