Hello, friend!
B525 is a consumer device.
B525 devices support IPv6 by default. That is, if downstream devices support IPv6, the B525 assigns IPv6 addresses to downstream devices by default.
If you want to disable the IPv6 address of a downstream device, disable the IPv6 address on the downstream device (PC or mobile phone).
Whether the B525 obtains an IPv6 WAN address depends on the network side. You can change the APN to enable the B525 to obtain only an IPv4 address.

Thanks!