HaSch:
I have a similar problem and I tried hard to make a sketch work on ATtiny85 with OLED1306 128x64 and U8g2lib.h. The sketch is compiling without any errors but after uploading to the ATtiny85 nothing is seen on the display. I tried several different constructors and varied many parameters but the OLED refuses to work.The display is ok, it works on Arduino UNO and Hello world example of U8x8 is displayed (Hello world example of U8g2 NOT). I tried several OLEDs with the same results.
What's going wrong?
Arduino IDE: 1.8.10, U8g2 Library: 2.26.14, OLED1306 with I2C interface
Now, I found the bug:
After line
u8g2.begin();
a new line has to be inserted:
u8g2.setPowerSave(0);
It seems that u8g2.begin() does not automatically switch off the power save mode.
Constructor has to be
U8G2_SSD1306_128X64_NONAME_1_SW_I2C u8g2(U8G2_R0,/* clock=/ 2, / data=/ 0, / reset=*/ U8X8_PIN_NONE);
for my display.