ryrona VoLTE/VoNR/VoWiFi uses SIP via IMS to implement calls via data. It goes through an IMS IPSec tunnel. It's the only way to have carrier-based on 4G and 5G or Wi-Fi. It's the same protocol for each once it's set up. The difference is how it sets it up. SMS can also be implemented via SIP and IMS but doesn't have to be. 2G/3G use an entirely different stack for calls which doesn't use data and is not used at all if you have 2G/3G disabled. They also use the legacy approach for SMS.
Based on the above details, we recommend using 4G-only, 4G/5G-only or 5G-only with VoLTE/VoNR rather than using 2G/3G and potentially having both the legacy and modern stack or just the legacy stack. It just makes more sense to use the modern code/protocols despite it being more complex and higher attack surface. The modern code is at least becoming more hardened and better written while the legacy code is not being improved and is going to be phased out. 2G and 3G are being shut down, so people might as well turn them off now if they have reliable 4G / 5G all the time. 4G-only will also have the best battery life in practice by using only a single protocol without switching between them, and 4G is still more efficient than 5G. 5G is more complex than 4G. 5G does have better cryptography but we recommend avoiding carrier-based calls/texts and using a VPN. Even without a VPN, nearly everything uses TLS.