SSD1306-based OLED display E/RD# and R/W# pins
The question is, should leave them floating when using I2C?


Use this "ER-OLED0.96-1 Series Interfacing Document" from the display manufacturer's page which you linked.

It includes the following I2C interface schematic, which shows those two signals E/RD# and R/W# are both grounded when using I2C, as I've marked in red on this extract from that document: