I am trying to record audio in Xavier NX without utilizing an external device (have reviewed similar post which suggested to use external device for this task). Due to requirements, I need to do such without it.
I have enabled I2S pins on my board according to this.
I connected 3.1 mm jack (speaker) to my PC and the other end of this wire was divided into three parts one of which corresponds to signal part and second to ground pin of Xavier.
Signal part was joined to pin 35 (I2S_FS), 38 (I2S_SDIN), 40 (I2S_SDOUT) and 12 (I2S_CLK) (using breadboard) of Xavier (brute-forcing).
I2S is a digital interface that requires a bit clock, frame clock and data. I assume that the output from the PC is analog and not digital and so that without first converting to digital this is not going to work. So yes you will need an external device to convert to I2S if you wish to the use the I2S interface.
Per the page you referenced before, these would be some options. Please note that the FE-PI modules are no longer available and but we have added support for the re-speaker 4-mic array.
Other users have used the PCM1863 codec and the PCM1865 codec but these require kernel and device-tree customisation and so do not work out of the box.