Hello,
Can the IPv4 devices communicate with the IPv6 device and the other way around?
IPv4 and IPv6 are two completely separate protocols, with separate, incompatible packet headers and addressing, and an IPv4-only host cannot directly communicate with an IPv6-only host.
No official workaround from Teltonika side.
However, I suggest you to check this link from OpenWRT documentation on IPv4/IPv6 communication, specifically 6in4 Tunnel / HE.net Tunnel Broker section.
Best regards,