All Samsungs that I know of have no VoLTE in custom ROMs as of now, something about it being hard to port over from the stock ROM - it would need to be reimplemented as opensource package (last I read, someone has a go at this), so it’s disabled anyway, even if you do not find the menu.
yes, similar, but authentication/register and IP encapsulation is different, involves a lot more telco acronyms in the outer layers, but gets more similar towards the “call itself” - addressing and voice data. VoWifi will be ipsec tunneled, but inside that tunnel its VoIP - same session protocol, same stream protocol. The posts here goes into more detail: