It does get confusing when Google, as the maker of Android, will not enable 5G profiles and VoLTE across the board in the OS itself, but is instead extremely selective to the point of being exclusive.
I think that's where the confusion lies for people - they see "5G" and assume the telco service will work especially since other Android phones work. But the concept of "telco profiles" is largely hidden from nearly all users.
While it's a given that there will be enough differences for telcos, there can always be the option to enable a "generic" profile for 5G and associated services like VoNR since it exists in the Android OS. Then it falls on the telco to fix it by supplying the relevant profile information either to Google directly or to the end users.