I've spent some time making two of my SSD1306 displays work with u8g2 library using two different i2c ports (Wire & Wire1) on Teensy 4.1 and wanted to share my experience.

The author of this library seems to assume that there is a #define WIRE_INTERFACES_COUNT 3 somewhere in the board definition and only then enables the functionality. Without it the U8G2_SSD1306_128X64_NONAME_F_2ND_HW_I2C constructor creates a no-op object.

The issue is mentioned here but in the context of Teensy 3.x and i2c_t3 (that does not support Teensy 4.x).

I worked around the problem by commenting out the relevant check in U8x8lib.cpp:
extern "C" uint8_t u8x8_byte_arduino_2nd_hw_i2c(U8X8_UNUSED u8x8_t *u8x8, U8X8_UNUSED uint8_t msg, U8X8_UNUSED uint8_t arg_int, U8X8_UNUSED void *arg_ptr)
// #ifdef U8X8_HAVE_2ND_HW_I2C
// #endif
  return 1;
Not sure if #define WIRE_INTERFACES_COUNT 3 is a standard practice but maybe it is worth adding it? I took a shot at it but I'm not sure where to put it, and platformio does not make it easy to edit those files.