Here you go, I2S output:

https://github.com/bschwind/rp2040-i2s/blob/e1d5647704b03ad1...

And I2S input:

https://github.com/bschwind/rp2040-i2s/blob/e1d5647704b03ad1...

The RP2040 has great documentation and the PIO is an amazing swiss army knife of a peripheral. I've had no trouble learning from their datasheet and docs and making plenty of PIO programs.