Dear all,
Will user see in GUI way to select network in case of 5G as for 2G its GSM, 3G WCDMA and for 4G LTE? What will be for 5G?
Mobile networks -> Data roaming
Using mobile data while roaming may result in additional charges.
It cannot be “5G Only” for sure. 
You can expect 5G NR.
What if he selected 5G NR and not opted any 5G plan, will network allow to use 5G BW?
In case of both where 4G as anchor for 5G NSA and for for 5G SA.
If I’m not mistaken you should be able to see 5G on GUI.
Assuming your Meta/MPSS builds are compliant with 5G, I’d try to deactivate mBN config files.
As last resource, try NV80000 = 64 for SA and 80 for NSA.
I believe, since 5G NR will be associated with LTE as the anchor or NR (SA) at least, there is a possibility that the user may see 5G selection as service(autoselect) and then the handset may be limited to 3 RATs at a time. 5G, and LTE. or maybe 5G, LTE, and WCDMA, if the OEMs are found having manufacturing boundations.