"Maximum how many devices can be connected to an i2c bus at a time"

Is a purely capacitive question

As long as the capaitance is low enough (related to the pullup resistor) you can add devices.

Thus the question has no absolute answer.

The correct answer is: "that depends"

I am, however, sure the questioner was looking for an answer of 128 which will be wrong, there is no way you can connect 128 devices without exceeding the capacitive load.

Ever so often, in an interview, you will come across an i.... that ask questions where, to be safe, you have to answer "you are looking for xxxx, but the answer is yyy because of zzzz.

Erik