Can the SX1509 I/O Expander be connected to the SparkFun Qwiic Mux Breakout - 8 Channel (TCA9548A)? If so, how should I do so.
Sure
You’d just use something like https://www.sparkfun.com/products/14425 and then follow the mux guide https://learn.sparkfun.com/tutorials/qw … troduction and the SX1509 guide https://learn.sparkfun.com/tutorials/sx … troduction