There might be, somewhere on this planet, be mobile service provider, that assign you your own public IPv4 address.
I know it is possible with Swisscom Business contracts and a special additional option.
For those specific cases this can be used. The thing is, the end device, in your case the 5G modem, doesn’t know if it’s behind a CG-NAT or not.
Please note, this has nothing to do with the functionality of the bridge mode. It might be possible to use bridge mode, but with the same limitations on the provider side.