that's not true. you can have IPv6 only in the backend and expose IPv4 only at the very frontend (like Cloudfare does the other way around).

Dual stack are not really needed and usually add complexity for few little benefits.

The main problem of IPv6 is the lack of people willing to learn it, teach it and adopt it.

Something brand new like Kubernetes should have from the start been IPv6 only , with IPv4 at the egress parts only.