Jek39d Try resetting cellular network settings and then reboot your phone: Settings app -> System -> Restore -> Reset cellular network settings.
If this does not help, contact your SIM card provider, so they can debug.
But, really, I wouldn't have cared. 4G is already super fast, up to 100 Mbit/s, and has better coverage and uses less battery. 5G is really oversold, it is a very marginal improvement over 4G, and probably not at all for indoor usage, which is where you likely are when you download much data.