Resolved! I-CUBE-wolfMQTT example code uses LwIP's sockets despite not using FreeRTOS.
I added I-CUBE-wolfMQTT and I-CUBE-wolfSSL software packs to my STM32CubeIDE project in CubeMX built into CubeIDE. In CubeMX I set parameters:for wolfSSL:RTOS - Single THreaded (no RTOS / Baremetal)IO interface - LWIP (native API)for wolfMQTT:FREERTO...