iPhone 12 5G not working

Okay so I was able to determine at least in my case what was causing the 5G to not work even though it was showing enabled on my phone on the top right. When I checked my VPN app in this case it was from Avast it was constantly switching on and off with 5G enabled. When I turned VPN off in the app settings (wouldn’t disable in the Apple “settings/VPN”) I then launched Apple maps and the navigation worked.

If you have your phone set to 5G and you aren't in an area where 5G service is available (which is a large part of the world at this time), you'd likely encounter this.

Go to Settings > Cellular > Cellular Data Options > Voice & Data

Make sure you have 5G Auto turned on or if you are in a location where 5G service is not at all available, go to LTE.

I believe this is a bug with the iPhone 12 while on 5G for Apple Maps. I experienced this today while in a confirmed 5G network area. I was able to surf in Safari on 5G and run apps that used 5G data. Though when trying to pull the navigation data from Apple Maps it stated it was unable to connect to the server. If I switched 5G off then it forced LTE and the maps would work, same over WIFi

I did in my response to you above. This is what I said:

Go to Settings > Cellular > Cellular Data Options > Voice & Data

Make sure you have 5G Auto turned on or if you are in a location where 5G service is not at all available, go to LTE.

5G coverage is very spotty, even in cities where it is deployed. So if you don’t have it on 5G auto whenever you lose signal you will run into this problem.

On a separate issue, using VPN is usually not a good idea→Don't use VPN services. · GitHub

VPN does not provide any benefit, and can actually reduce your privacy because the VPN provider knows everything about your Internet use. And many VPN providers are in the business of selling that information. Including Avast → Avast is spyware

You're welcome and I hope it helps you.