I need to update iOS without Wi-Fi

You likely have AT&T as your carrier? 5Ge is NOT actually 5G service. It is what AT&T calls Edge, and is nothing more than marketing, but it ISN'T 5G. It is a misleading name for an advanced LTE (4G) service. When you go to Settings > Cellular > Cellular Data Options > Voice & Data

What does it show there? In order to update over cellular, you need to be paying for true 5G Cellular Service AND actually be on 5G at the time you want to update your iPhone.

OK. So you do have 5G service. You're just not in a location where you're currently on 5G. Until you change to a location where you have true 5G service, you can't update using cellular. You can go to a Starbucks and use their Wifi to update your iPhone. You can go to an Apple Store and use their Wifi. You can update using a computer with iTunes (Windows) or Finder (Mac). But you cannot update over cellular on 5Ge.

If you have 5G cellular service on your phone, you can update using Cellular. If you don't have 5G service, you can't update without Wifi.

You will have to use a 5G cellular connection, to be able to download and install iOS updates without using Wi-Fi.

You can update through your computer. See the links here: Update your iPhone or iPad - Apple Support

Mine updated over cellular just fine on iOS 17.4, so 17.4 isn't the issue. Do you actually pay for 5G service and where are you located?

You're very welcome.