I work in mobile phone sector.
Starting with the S8/Note8, Samsung has removed the baseband chips (actually has never included it in the factory) so even if you manage to flash it with stock firmware, it will never pick up a signal no matter what you do. And no, you can't solder in the baseband chips, they are custom chips and extremely difficult to solder being fine pitched surface mounts.
You best option is to try to flash it with the latest stock firmware, disable the MDM security, and use it on WiFi only.
By the way, the N950"X" version is not even a US Qualcomm model, but an international Exynos based main board, so don't waste your time trying to flash the "U/U1" firmware. Try the international "F" version, but most likely it will only accept the specially modified "X" firmware.
Which f firmware you Installed please give me tutorial please:crying:
Thanks for your experience. I am stuck with same case. I have been trying to install the F version on the US Galaxy S9+. The greater problem my LDU has is that the date is incorrect and no settings is enabled to allow me make any adjustment. Every necessary settings greyed out. Odin flash attempts all failed and Samsung Kies will always say I should enable USB debugging to even see and recognize my device but that option in developers mode is all greyed out and not allowing enabling. Same thing with factory reset not allowed. What can I do to at least use the Wifi because now it cannot connect due to incorrect date setting still whowing March 2018?