My 5G

Then contact your carrier for help with their service.

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

If you're not seeing 5G on the display, I'm guessing that there there could be several reasons for it:

• You haven't paid for cellular service – or at least, not for cellular service from a carrier that supports 5G.
• You're in an area where your carrier has poor coverage for 5G.
• Something is broken in your iPhone and it needs hardware service.

My guess is that it is most likely to be a coverage issue – something you need to contact your phone company (carrier) about.