It's not new. You can get private address space that's routed into your network, but if you trust telco network security, you probably don't have anything worth protecting (or run a VPN over the top and only use the private APN for persistent IP addressing).

For example, AT&T's private APN service has been around since the 3G days: https://www.business.att.com/products/private-mobile-connect...

This requires a physical cell tower and 5G receiver so it’s not as flexible as running a VPN client on your laptop.