olikraus:
Thanks for the u8g2 logo picture. I think the display is brocken: The second half of the internal display RAM does not work. Your display should work correctly with U8G2_SSD1306_128X64_NONAME_1_HW_I2C constructor, but it doesn't.Yet I still have some doubts: Are you sure it is a 128x64 display? It looks more like 96x48 version.
Oliver
I tried 96x48 and other resolutions, either black or heavily wrapped around texts.
Like you, I suspected it was broken. I will go for a new display and be back in one and a half hour with the result.