In order to mix and match you need some intermediary server that has both IPv4 and IPv6 to translate.
For example my mobile service provider (T-Mobile US) doesn’t support IPv4 on their network, however I can still access IPv4 services because they automatically route that traffic through a NAT64 server, which translates the IPv6 from my device into IPv4 heading to the IPv4-only service.
T-Mobile actually takes it a step further than many other IPv6-only service providers. NAT64 alone only solves problems with servers that are IPv4-only, whereas T-Mobile uses 464xlat (which includes NAT64) which also solves problems with apps on the user’s device that are IPv4-only.
IPv6 clients can communicate with IPv6 servers.
IPv4 clients can communicate with IPv4 servers.
In order to mix and match you need some intermediary server that has both IPv4 and IPv6 to translate.
For example my mobile service provider (T-Mobile US) doesn’t support IPv4 on their network, however I can still access IPv4 services because they automatically route that traffic through a NAT64 server, which translates the IPv6 from my device into IPv4 heading to the IPv4-only service.
T-Mobile actually takes it a step further than many other IPv6-only service providers. NAT64 alone only solves problems with servers that are IPv4-only, whereas T-Mobile uses 464xlat (which includes NAT64) which also solves problems with apps on the user’s device that are IPv4-only.