Why???
Maybe if you numbered BOTH arrays and BOTH indexes, so you KNOW that you are not mistakenly using the wrong index with an array.
button = analogRead(analogButton);
button2 = analogRead(analogButton2);
So you can read that a switch is barely pressed, halfway pressed, really mashed?
Just what ARE you reading?
// read from the sensor:
readings[readIndex] = volume;
That is NOT what the code does. Your array to average the volumes has a really stupid name!
readings2[readIndex2] = sht1x.readTemperatureC() + 5;
Another example of a useless name!