ProfessorMonks It might be a bit of a stretch to explain why 5G is recommended. But let's start with the basics. A lower frequency means a longer wavelength. A longer wavelength means greater range and less susceptibility to interference from obstacles. The old classic pager is still very popular in medicine because it operates at lower frequencies, and these waves can penetrate medical buildings, which are often additionally protected due to the sensitivity of medical equipment (e.g., MRI scanners). Longer wavelengths can also reflect off the ionosphere, generally providing very long ranges without the need for multiple transmitters (towers). Unfortunately, a longer wavelength means less information can be transmitted. As more and more data is transmitted, the trend for many years has been towards higher frequencies, which allow for greater throughput. LTE is therefore faster than 3G, but requires more towers, and 5G is even faster than LTE, but requires very dense transmitter coverage and is highly susceptible to interference. 5G is therefore more available in large metropolitan areas, but you may have coverage issues if you're outside of heavily urbanized areas. This may mean you'll still need LTE. Consider the same thing with your home Wi-Fi. 2.5G has greater range but lower bandwidth than 5G.
However, a higher frequency is havier for the modem, which means greater battery drain and overheating. In practice, however, 5G will use less power than LTE when transferring a large file because the transfer time will be shorter (but the phone will be more heavily loaded and heat up more). Therefore, if you're not transferring large files, LTE is more recommended.
When it comes to security, in theory, 5G is safer. In practice, this may vary, as 5G is a new solution and is still being implemented. You can find a lot of information online about the differences between 5G and LTE, so I won't go into detail.
Personally, I prefer Wi-Fi only phone and an external mobile LTE modem, which is used only when absolutely necessary. I don't know of any LTE modem that's sufficiently secure.