for the I2C use:
#define SDA 12
#define SCL 11
U8G2_SSD1306_128X64_NONAME_F_SW_I2C u8g2(U8G2_R0, /* clock=*/ SCL, /* data=*/ SDA, /* reset=*/ U8X8_PIN_NONE);
for SPI use:
U8G2_SSD1306_128X64_NONAME_F_4W_SW_SPI u8g2(U8G2_R0, /* clock=*/ 8, /* data=*/ 10, /* cs=*/ 7, /* dc=*/ 9, /* reset=*/...