I googled for I2C-scanner multiple I2C-adresses.
One thread mentions that there are no pullup-resistors
Well I would be very astonished if there are no I2C-pullup-resistors on this display.
Do you have two 4k7 resistors laying around?
Do you have any other I2C-device laying around?
This would be good for testing if the I2C-bus works at all.
Another option is to use the most shortest wires that you have for connecting the OLED-display with the pico