Yes, I am aware of the datasheet, but we’ve never had any problem using 3.3V ESP8266 to drive 5V PCA9555. If you believe it’s a problem you can simply add a diode in series between 5V and PCA9555’s VCC pin, so that will drop 0.7V and supply 4.3V to PCA9555. This way 3.3V/4.3V > 75%.
