How to activate 5G

Adding to ChrisJ4203’s thoughts, when I got my first 5G iPhone, I noticed I could not see the 5G options until I chose a 5G plan from my carrier (AT&T).

Make sure you have a 5G plan (assuming you want one, and your carrier offers one).

Have you contacted your cellular provider?

Have you obtained a new 5G capable SIM card?

Are you in a region with 5G coverage?

That is probably because your carrier does not provide 5G yet, or you need to get a new SIM from them that handles the 5G. Check with the carrier. They are also the one that controls the settings in the Cellular section of Settings.