Hey there the problem is due to the low ram storage of the microcontroller you are using adafruit ssd1306 and GFX uses around 1kb of ram for allocation for the size of 128*64 if you don't have 1kb of dynamic memory after compilation it will not be able to allocate memory for OLED.The solution is used of different library as you are not using graphics like U8G2 to work with the OLED. Limitation is you will not be capable of displaying graphics..