Booting to the pre-install environment was the goal to finger obvious hardware/stability issues. Something that lands you on a desktop. If you want to try installing - whatever distro it was - check a guide for it. Fedora and Ubuntu are good places to start for both of these routes. They should require minimal configuration if you don't care about secureboot etc.
I think it's most likely a Windows issue based on what was presented, but it's good to make sure the hardware is OK. It costs nothing but a little time.
Can you boot to USB? Using something other than Windows may also help determine that the hardware is working. If everything seems to work, it could be an issue with the boot entries on your main board, corruption on the disk, or something wrong with the disk physically. If you use Linux, whatever the latest Fedora version is will probably support newer graphics cards such as a 9070xt.
This was years ago - but I feel like the solution for CGNAT at the time required a static, and we also implemented DDNS for their TLD. It definitely wasn't T-Mobile. It took some time to find someone at the mobile ISP who understood what we needed, and what options existed.
If you don't have specific application support needs, Debian based distros like Ubuntu/Mint (based on Ubuntu) are good for a first-timer. You won't have all the GUI management stuff like you get in Windows. You may find Arch a bit more challenging.
ISP may offer a static IP, and/or help bypassing CGNAT if either are useful. I've done it for a 5G failover with VPN, with the gateway in passthru, and a firewall behind it. At a glance, it looks like the FX4100 supports all of this
It's almost like the place is run by psychopaths and narcissists.