something I have not been able to find in in the datasheet, so I measured it.
it's weak pull-up approx 6kohms at 3.3V and 25degrC typical.
if you want to use the GPIO pin as mute driver at startup there are 2 solutions:
1- make sure the mute driven logic is active high.
2- or if not load the line with 1Kohms. if the power is a problem a 22uf will do as well as I saw 25msec duration of the mute high at 96khz frame rate and 24Mhz xtal clock. it can be longer depending on the startup time of the oscillator.