The original font6x14.h often declares the array as const uint8_t font6x14[] PROGMEM; but define the array in the header. You must either:
// Data for Exclamation Mark (ASCII 33) 0x00, 0x00, 0x04, 0x00, 0x04, 0x00, 0x04, 0x00, 0x04, 0x00, 0x00, 0x00,
To confirm the library version from 2021: